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A215147 For n odd, a(n)= 1^2+2^2+3^2+...+n^2; for n even, a(n)=(1^2+2^2+3^2+...+n^2) + 1. 0
1, 2, 5, 6, 14, 15, 30, 31, 55, 56, 91, 92, 140, 141, 204, 205, 285, 286, 385, 386, 506, 507, 650, 651, 819, 820, 1015, 1016, 1240, 1241, 1496 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Square pyramidal numbers when n is odd .

An interleaving of A000330 and A056520. - Michel Marcus, Aug 07 2013

LINKS

Table of n, a(n) for n=1..31.

Index entries for linear recurrences with constant coefficients, signature (1,3,-3,-3,3,1,-1).

FORMULA

a(n) = (6*(5+3*(-1)^n)+(13-9*(-1)^n)*n-3*(-3+(-1)^n)*n^2+2*n^3)/48. G.f.: -x*(x^6-x^5-2*x^4+2*x^3-x-1)/((x-1)^4*(x+1)^3). [Colin Barker, Nov 16 2012]

MAPLE

for i from 1 to 100 do a(2*i-1):=sum('k^2', 'k'=1..i);

a(2*i):=a(2*i-1)+1; end do;

CROSSREFS

Sequence in context: A105043 A083095 A083097 * A191229 A191120 A245540

Adjacent sequences:  A215144 A215145 A215146 * A215148 A215149 A215150

KEYWORD

nonn,easy

AUTHOR

Kritsana Sokhuma, Aug 04 2012

STATUS

approved

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Last modified May 31 00:53 EDT 2020. Contains 334747 sequences. (Running on oeis4.)