Nagel has been successfully sued five times for child support

Women have found Nagel on Craigslist, donor sites and by word of mouth

The hopeful mother then places the cup in her cervix for 12 hours

He often produces the sperm in a restroom in a menstrual cup

Professor Ari Nagel, 40, is the proud father of 22 children. All but one came from sperm he donated for free to single women and lesbian couples

A New York math professor is the proud father of 22 children, many of whom were conceived in restrooms at Target or Starbucks.

But you won't find another woman in the stall with Ari Nagel. The single professionals and lesbian couples he offers his services too are waiting outside - for a cup of his sperm.

Nagel has been donating his sperm to women for nearly a decade. He's now got nearly enough children to fill a baseball team, and 18 baby mamas to call his own.

The Kingsborough Community College professor's first donation happened eight years ago at a fertility clinic, with a single friend in her late 30s who wanted to become a mother.

Women have since found Nagel via Craigslist, word of mouth or Known Donor Registry, a free website connecting couples to donors who do not want to remain anonymous.

It's an option that runs much cheaper for hopeful mothers than a sperm bank, where costs can range anywhere from $300 to $4,000, according to the American Pregnancy Association.

Nagel offers his sperm up for free. Sometimes he and the mother-to-be will conceive the old-fashioned way, with lesbian couples sometimes holding their partner's hand in bed for moral support.

But more often Nagel's sperm is produced thanks to a couple minutes of alone time with his cell phone, and delivered into a menstrual cup an ovulating woman can then insert in her cervix for up to 12 hours.

And the women don't just flock to Nagel because of his free services or high sperm count.

'He's a lot of fun to be around,' Tiffany Harrison, 41, told the New York Post. 'He loves people, he's outgoing, and he's gorgeous.'

Harrison and her wife Yvonne have a toddler daughter with Nagel, one of his many children the father regularly sees for babysitting, birthdays and graduations.

Nagel has been donating his sperm to women for nearly a decade. He's now got nearly enough children to fill a baseball team, and 18 baby mamas to call his own

Nagel often produces his sperm in a bathroom at Target or Starbucks before handing it off in a menstrual cup to a hopeful mother, who can then insert it into her cervix for up to 12 hours

Nagel said he loves that his side hobby allows him to have a huge family without all the responsibility. Some children he'll see every week, but there are others he's never even met.

'I feel like I'm getting all the joy, but also getting a good night's rest,' he told the Post.

But some mothers haven't been happy with Nagel's hands-off approach, and have taken him to court.

The first five women that Nagel provided his services to successfully sued him for child support, although he claims they promised in advance they would never sue.

'I don't know what's more surprising: that five sued or 17 didn't,' Nagel said. 'They were all well aware there was no financial obligation on my part.'

Crystal, who has two sons with Nagel, said she had been under the expectation that they would co-parent together and feels her kids got 'left in the dust'.

Despite losing half of his paycheck to his growing brood, Nagel is still talking to more women looking to have children.

'This isn't time-consuming, and I'm doing it anyway,' he said. 'It's very easy for me to do.'

And Nagel said he has no regrets when it comes to the family now spread across the world.

'I just love seeing how happy the moms and kids are. That's why I do this,' he said.