Number of subsets of {1,2,3,...,n} that sum to 0 mod 15.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =5a(7) =9a(8) =18a(9) =36a(10) =70a(11) =138a(12) =276a(13) =548a(14) =1096a(15) =2192a(16) =4374a(17) =8744a(18) =17486a(19) =34958a(20) =69916a(21) =139830a(22) =279630a(23) =559260a(24) =1118520a(25) =2236988a(26) =4473964a(27) =8947920a(28) =17895736a(29) =35791472