A024391 - OEIS

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A024391

2nd elementary symmetric function of the first n+1 positive integers congruent to 2 mod 3.

10, 66, 231, 595, 1275, 2415, 4186, 6786, 10440, 15400, 21945, 30381, 41041, 54285, 70500, 90100, 113526, 141246, 173755, 211575, 255255, 305371, 362526, 427350, 500500, 582660, 674541, 776881, 890445, 1016025, 1154440, 1306536, 1473186, 1655290

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..34.

Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

FORMULA

a(n) = n*(n+1)*(3*n+2)*(3*n+5)/8.

O.g.f.: -x*(10+16*x+x^2)/(-1+x)^5 . - R. J. Mathar, Feb 14 2008

MATHEMATICA

LinearRecurrence[{5, -10, 10, -5, 1}, {10, 66, 231, 595, 1275}, 50] (* Harvey P. Dale, Aug 19 2019 *)

CROSSREFS

Sequence in context: A269679 A211056 A269468 * A074362 A080421 A320817

Adjacent sequences: A024388 A024389 A024390 * A024392 A024393 A024394

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling

STATUS

approved