Number of arithmetic subsequences of [1..n] with length > 1.

Terms

a(0) =0a(1) =1a(2) =4a(3) =9a(4) =17a(5) =27a(6) =41a(7) =57a(8) =77a(9) =100a(10) =127a(11) =156a(12) =191a(13) =228a(14) =269a(15) =314a(16) =364a(17) =416a(18) =474a(19) =534a(20) =600a(21) =670a(22) =744a(23) =820a(24) =904a(25) =991a(26) =1082a(27) =1177a(28) =1278a(29) =1381