On a recent Wednesday evening, 13 fifth- to ninth-grade students from around Marin County gathered in a Dominican University classroom for an after-school activity that didn't involve sports or the arts.

Instead, the students sat hunched over note paper trying to figure out a complicated math problem as part of the weekly Marin Math Circle program.

"I just really enjoy doing the more advanced math," said Sam Toland, a 12-year-old seventh-grader at Mill Valley Middle School who has been attending the math circle since it started in September 2009.

"You get to listen to college professors and different professors every time," he added. "Sometimes you can work on a problem for the whole class. ... It's more advanced, but also it's just different."

Math circles, enrichment programs that originated in Russia and Eastern Europe, exist throughout the Bay Area and country, with groups meeting regularly in Berkeley, San Jose and at Stanford University. Mill Valley parents Jon and Nancy Sigerman started the Marin Math Circle in 2009 after Jon attended a teaching workshop at the Mathematical Sciences Research Institute in Berkeley.

The couple then approached Sibdas Ghosh, chairman of Dominican's natural sciences and mathematics department, with the idea of holding sessions at the university. Ghosh agreed, and Dominican math professor Linda Green stepped in to serve as the circle's director.

The goal is "to expose students to a variety

of topics in math that they wouldn't see in middle school, high school or maybe even college," as well as boost problem-solving techniques and the quality of their explanations, Green said.

Some 15 to 40 students attend each week, with topics ranging from four-dimensional geometry to game theory, Jon Sigerman said. Visiting professors and instructors receive a small honorarium, which is financed by a Mathematical Sciences Research Institute grant and parent contributions.

Organizers hope to increase enrollment so they can divide the circle into elementary, middle and high school groups, Sigerman said.

On Wednesday, instructor Joshua Zucker taught a lesson on digit sums, and students attempted to make a total of 100 by adding numbers whose digits only consist of zero and eight. The idea was to get to 100 using the fewest numbers possible.

"You can conclude that 100 is not possible because it's not a multiple of eight," said 9-year-old Nico Brown, a fifth-grader at Edna Maguire Elementary School in Mill Valley.

"But it could be because you could use decimals," replied Cole Bouton, a 13-year-old seventh-grader at Kent Middle School in Kentfield.

A group of parents — and professor Ghosh — sat in the back of the room, also working on the problem.

"The participation is juicy — it's not dry," Ghosh said with a smile.

While students need only be interested in math to participate, some have gotten frustrated and dropped out early on because the discussions can be advanced, Sigerman said.

"Imagine these kids having to sit in class and do fractions and times tables," he said. "It's torture."

After Zucker switched the digits to zero and seven, Nico quickly came up with a solution.

"He really likes math, and we're struggling to meet his needs," said Nico's father, Ian Brown, of Mill Valley. "I can entertain him with adult-like questions, but I can't go into math with him.

"There are so many options for kids who are outstanding say in gymnastics or tennis — there's all sorts of structure for them," Brown said, noting that things aren't so simple when your 9-year-old idolizes mathematicians and wants to discuss quantum mechanics.

"I know all the math they're teaching us at school," Nico said.

Meanwhile, the Sigermans' son, Max, said he appreciates the math circle's spirit of collaboration.

"The group aspect of it is nice especially when there are people you know there," said Max, a 13-year-old eighth-grader at Mill Valley Middle. "You can collaborate with them, and you can share your ideas as opposed to just individual work, which isn't as interesting or fun."

For information on the Marin Math Circle, visit www.marinmathcircle.org.