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 A181440 a(1) = 2; for n > 1, a(n) = A000217(n)-(sum of previous terms). 3
 2, 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 2 followed by A065475, or A000027 with first and second term interchanged. It can be observed that this sequence is an "autosequence", that is a sequence which is identical to its inverse binomial transform, except for signs. More precisely, it is an autosequence "of the second kind", since the main diagonal of the successive differences array is twice the first upper diagonal. - Jean-François Alcover, Jul 25 2016 LINKS OEIS Wiki, Autosequence Wikipedia, Autosuite de nombres (in French). FORMULA G.f.: x*(2-x)*(1-x+x^2) / (1-x)^2. - Joerg Arndt, Jul 25 2016 MATHEMATICA a = {2}; Do[AppendTo[a, ((n^2 + n)/2) - Total@ a], {n, 2, 72}]; a (* Michael De Vlieger, Jul 25 2016 *) PROG (MAGMA) S:=[2]; s:=2; for n in [2..80] do a:=Binomial(n+1, 2)-s; Append(~S, a); s+:=a; end for; S; CROSSREFS Cf. A000027 (natural numbers), A000217 (triangular numbers), A065475 (natural numbers excluding 2). Sequence in context: A283069 A304528 A175499 * A035043 A288118 A155963 Adjacent sequences:  A181437 A181438 A181439 * A181441 A181442 A181443 KEYWORD easy,nonn AUTHOR Giovanni Teofilatto, Oct 20 2010 EXTENSIONS Edited by Klaus Brockhaus, Oct 26 2010 A171950 and A181440 are two different edited versions of a sequence submitted by Giovanni Teofilatto. - N. J. A. Sloane, Oct 29 2010 STATUS approved

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Last modified December 14 12:04 EST 2019. Contains 329979 sequences. (Running on oeis4.)