a(n) is the number of sets modulo n which can be formed by a finite arithmetic sequence.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =31a(5) =42a(6) =99a(7) =119a(8) =193a(9) =218a(10) =463a(11) =340a(12) =807a(13) =682a(14) =849a(15) =1087a(16) =1939a(17) =1299a(18) =2775a(19) =1862a(20) =2615a(21) =3050a(22) =5107a(23) =2988a(24) =5681a(25) =5242a(26) =6439a(27) =5656a(28) =10615a(29) =5562