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A151980 Numbers n such that n^2 - n is divisible by 20. 3
0, 1, 5, 16, 20, 21, 25, 36, 40, 41, 45, 56, 60, 61, 65, 76, 80, 81, 85, 96, 100, 101, 105, 116, 120, 121, 125, 136, 140, 141, 145, 156, 160, 161, 165, 176, 180, 181, 185, 196, 200, 201, 205, 216, 220, 221, 225, 236, 240, 241, 245, 256, 260, 261, 265, 276, 280, 281, 285, 296 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..60.

Index entries for linear recurrences with constant coefficients, signature (1,0,0,1,-1).

FORMULA

G.f.: x^2*(1+4*x+11*x^2+4*x^3)/((1-x)^2*(1+x)*(1+x^2)). [Colin Barker, Jan 14 2012]

a(n) = a(n-1)+a(n-4)-a(n-5). [Colin Barker, Nov 29 2012]

CROSSREFS

Sequence in context: A298150 A238586 A195958 * A063612 A269969 A057281

Adjacent sequences:  A151977 A151978 A151979 * A151981 A151982 A151983

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Aug 23 2009

STATUS

approved

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Last modified January 18 13:09 EST 2019. Contains 319271 sequences. (Running on oeis4.)