

A131179


a(n) = if n mod 2 == 0 then n*(n+1)/2, otherwise (n1)*n/2 + 1.


3



0, 1, 3, 4, 10, 11, 21, 22, 36, 37, 55, 56, 78, 79, 105, 106, 136, 137, 171, 172, 210, 211, 253, 254, 300, 301, 351, 352, 406, 407, 465, 466, 528, 529, 595, 596, 666, 667, 741, 742, 820, 821, 903, 904, 990, 991, 1081, 1082, 1176, 1177, 1275, 1276, 1378, 1379, 1485, 1486
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OFFSET

0,3


LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
Index to sequences with linear recurrences with constant coefficients, signature (1,2,2,1,1).


FORMULA

G.f.: x*(1+2*xx^2+2*x^3) / ( (1+x)^2*(x1)^3 ).  R. J. Mathar, Sep 05 2012
a(n) = ( n^2+1+(n1)*(1)^n )/2.  Luce ETIENNE, Aug 19 2014


PROG

(Haskell)
a131179 n = (n + 1  m) * n' + m where (n', m) = divMod n 2
 Reinhard Zumkeller, Oct 12 2013


CROSSREFS

Cf. A128918.
Sequence in context: A200816 A047341 A091910 * A079353 A242654 A243681
Adjacent sequences: A131176 A131177 A131178 * A131180 A131181 A131182


KEYWORD

nonn,easy


AUTHOR

Philippe LALLOUET, Sep 16 2007


STATUS

approved



