Number of arithmetic progressions in {1,2,3,...,n}, including trivial arithmetic progressions of lengths 1 and 2.
1, 3, 7, 13, 22, 33, 48, 65, 86, 110, 138, 168, 204, 242, 284, 330, 381, 434, 493, 554
1 seqfan posts
Fri Dec 26 23:06:26 CET 2008 [seqfan] Some items inspired by appearances of 2009 in the OEIS