At a gathering of students, teachers and family members at Stuyvesant on Wednesday, David Linker, a former colleague and Mr. Geller’s longtime friend, told an audience of about 200 that Mr. Geller was a low-tech kind of guy who rarely kept his cellphone on.
A Stuyvesant math teacher, Maryann Ferrara, who worked with Mr. Geller for 17 years, said he was a foodie who once brought her a piece of baked lemon tart to try.
Still, it was Mr. Geller’s son, Jason Geller, 40, from the Upper West Side, who reminded the group of his father’s true passion: teaching.
“At 2 a.m. he woke up,” said Jason Geller, referring to the night before his father died. “He looked up at me and said, 'Take one and pass it down, take one and pass it down; are there any questions?' ”
The story drew a mix of tears and applause.
In the hallway, quiet tributes to Mr. Geller were piling up. A photocopied portrait was pinned to a board covered in black fabric. Copies of the school newspaper, The Spectator, which featured a front-page article on Mr. Geller, sat in a stack nearby.
To the side was a patchwork of personal messages written on red and blue foam squares — many containing Mr. Geller’s mantra, “Math is No. 1.”
His brother, Harold A. Geller, 57, from Burke, Va., a professor at George Mason University, wore a deep red tie printed with several math-related equations, like the formula for finding the area of a polygon.
Harold Geller said he bought several math ties shortly after Mr. Geller was found to have melanoma and wore one every time he visited his brother in the hospital.
“ 'I like the tie,’ that’s what he said,” Harold Geller said. “The Gellers are not big on words unless we’re teaching.”
Before stepping down from the stage, Jason Geller took the T-shirt he received after running last weekend’s ING New York City Marathon, held it up for everyone in the theater to see, and read aloud the words printed on the back: “New York is #1, Math is #1 and My Dad is #1!”