SINGER-songwriter Tristan Prettyman’s lucky number should be 23. “My brother introduced me to the 23 Enigma, a theory that 23 is cosmically very magical,” says the 23-year-old San Diego native. “After he told me about it, it started appearing everywhere.”

The number has made such an impression on her that she even named her debut album “twentythree.”

“I was turning 23 on May 23rd this year, so it just made sense – maybe this’ll be a lucky year for it,” she says. Plus, “I had many goals set for the time I turned 23, including having my record out.”

Fortunately, things are working out, thanks in large part to her parents, who supported her dropping out of college to pursue music.

Three years ago, she was on her way to getting a major in business communications, aiming to be a clothing rep in the surfing industry.

But one day, “My parents came to a show and were amazed by the audience’s reaction. They said, ‘We really think you should take a break and see if this is what makes you happy,'” says Prettyman. “[Before that] my dad was always like, ‘Get good grades, go to college, graduate and go into the real world.’ But now they’ve both started surfing and are waiting for me to get a beach house so they can come and visit.”

All this talk of surfing, combined with her mellow, folky and acoustically driven album, is bound to bring up comparisons between Prettyman and another surfing singer-songwriter – Jack Johnson. Turns out they’re old friends.

“We met long ago, when I dated a friend of his,” says Prettyman, who’s currently seeing musician Jason Mraz. “Early on, Jack was one of the people who’s steered me, helped me stay on my own path.”

Along that path, Prettyman waded into the deep end, touring with artists G. Love, Gavin DeGraw and the John Butler Trio (with whom she’s playing on Friday at Webster Hall).

“I was lucky to be given the opportunity to go the fast route and was forced to learn quickly – I’m definitely catching up.”