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1, 1, 1, 1, 2, 5, 15, 53, 222, 1078, 5994, 37622, 262776, 2018305, 16873364, 152233518, 1471613387, 15150569446, 165269824761, ...

There is a lot of information in the Sloan The On-Line Encyclopedia of Integer Sequencespage.

show/hide this revision's text 1

1, 1, 1, 1, 2, 5, 15, 53, 222, 1078, 5994, 37622, 262776, 2018305, 16873364, 152233518, 1471613387, 15150569446, 165269824761, ...

There is a lot of information in the Sloan Integer Sequences page