Time for some magic, Yossi Elran announced to a full house of students, teachers and parents from three area day schools gathered last week at the Jewish Community Services Building in Center City.

The visiting Israeli mathematician pulled on an eye mask as a blindfold and called up a volunteer to write any three-digit number on the chart behind him, then reverse the order of the digits and subtract the smaller number from the larger.

Now, he continued, reverse the digits of the result.

"So if your number was 198, you should write 891 under it," he instructed, hitting it exactly. The crowd gasped.

"How did he do that?" one child exclaimed. "Are you a robot?" another shouted.

Elran didn't miss a beat. This time, he said, add the two numbers. He held up a piece of paper with 1,089 written on it before the boy behind him could even finish coming up with that answer.

The scene was proof of Elran's conjecture that math can -- and should -- be fun. He's been building on that premise as the Israel-based international director of an extracurricular math program conceived at the Weizmann Institute of Science in Rehovot 30 years ago.

The program, Math by Mail, is relatively new to most of the kids who were gathered here. Forget the stigma of the math nerd -- among Torah Academy, Politz Hebrew Academy and Abrams Hebrew Academy, roughly 100 kids have not only joined in the supplementary mathematics activities, their parents even pay $100 extra for them to do so.

Abrams parent Michelle Schachter said it's well worth the money to see her two children excited about doing math at home.

"They're being challenged -- different challenges than what they're getting at school," said Schachter, of Yardley.

Technically, Math by Computer would be a more accurate name for the program, but when it first started in Israel, the students received paper worksheets that they sent by snail mail to Weizmann for feedback.

When Elran took over 12 years ago, he updated the curriculum for an online platform to make it more interactive and entertaining. Animated characters accompany word problems, puzzles and games; and students can log into forums and chat rooms to get help from each other or from professional mathematicians at Weizmann's Davdison Institute of Science Education.

Over the course of the academic year, participants in grades 3 through 9 get four "booklets" on topics ranging from "dimensions" to the "game of life." Each comes in three levels and four languages: Hebrew, Arabic, English and even Spanish. Instead of mailing responses, students submit them through the website for grading and comments from the Israeli mathematicians. The problems are also available in printed booklets for those who don't have access to computers.

Altogether, the program now counts 2,000 participants in Israel and another 1,000 in Canada, Australia, Romania, Brazil, Mexico and Philadelphia -- the first place it's made an American appearance.

That happened completely by accident, said local program coordinator Irene Eizen, recounting how she met Elran, who handed her one of the booklets during a July 2010 Israel tour of initiatives supported by the Philadelphia-based Lasko Family Foundation.

"I became so engrossed in the problems," said Eizen, a former math supervisor for the Lower Merion School District who now teaches education at Temple University.

Eager to test the content in the states, Eizen started a pilot at Abrams in January, first with the printed booklets and then online with the addition of a new school computer lab this fall. While the problems can be completed independently, Eizen comes to the school once a week to guide the 56 participants during their "club" period. She does the same thing for Torah Academy and Politz, which both started this fall with about 30 and 15 kids, respectively. The schools pay a stipend for her time, she said, because the $100 registration fee goes directly to Math by Mail. Students with financial need can apply for scholarships through Eizen's nonprofit Foundation to Achieve Mathematics Excellence.

Ten-year-old Ari Hilibrand, a fifth-grader, is among the group of math devotees who just started the first "Vampire Numbers" lesson at Torah Academy.

"It helps you with math in a fun way," Hilibrand said.

Aside from making the kids think outside the box, it gives them the tools to attack any problem, said Janet Zuazo, a fourth grade math teacher at Abrams. "Before, they didn't know where to begin."

Eizen cautioned that Math by Mail isn't a substitute for curricular math, but it's a great way to help kids "think like a mathematician" because they use higher-order thinking to solve problems. According to national reports, she said, those are the kinds of critical skills that American kids often lack.

Elran agreed. This is the kind of enrichment that gets kids "to think about the problem, not just do rote work, and it will teach them to enjoy math and not become afraid of math."

Over the hour-and-a-half-long Nov. 1 presentation in Philadelphia, Elran dove from one math puzzle to the next to demonstrate just how cool basic addition, palindromic numbers and the spatial properties of math could be.

The students "oohed" as he shifted the images on a flexagon, a piece of paper with more than two faces, and applauded as he filled in a four-by-four "magic square" so that every row, column, diagonal and even quadrant added up to 92. Then, it was their turn to solve a similar puzzle on a smaller scale.

"I'm going to be in trouble with the magicians' association because a magician never reveals his secrets," Elran joked after explaining a shortcut to completing the square.

He didn't give away all his secrets, though, leaving students to figure out how he predicted the one-digit outcome of a pyramid addition problem.

Stumped, a group of eighth graders from Abrams begged him for a hint after the presentation.

"We tried every answer, we can't figure it out. Will you tell us?" pleaded 13-year-old Heather Brandspiegel. Elran grinned and shook his head, inviting them to email him later if they couldn't get it.

Lindsay Chevlin, 13, recalled how she, Heather and a few other friends recently spent their entire lunch and recess trying to crack a previous puzzle. When they finally had it, they ran through the school to find Eizen -- only to be told that their answer was wrong. So they went back to work until, finally, everything clicked. "It was like, 'Whoa, I've never seen that before,' "she said. "It's nice having that light-bulb moment."