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A195917 Numbers n such that both n+1 and 7n+1 are squares. 2
0, 24, 120, 6240, 30624, 1585080, 7778520, 402604224, 1975713600, 102259887960, 501823476024, 25973608937760, 127461187196640, 6597194410303224, 32374639724470680, 1675661406608081280, 8223031028828356224, 425611400084042342040, 2088617506682678010360 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..832

Index entries for linear recurrences with constant coefficients, signature (1,254,-254,-1,1).

FORMULA

a(n) = A161852(n)^2-1.  - Bruno Berselli, Oct 28 2011

G.f. -24*x^2*(1+4*x+x^2) / ( (x-1)*(x^2-16*x+1)*(x^2+16*x+1) ). - R. J. Mathar, Nov 04 2011

MATHEMATICA

LinearRecurrence[{1, 254, -254, -1, 1}, {0, 24, 120, 6240, 30624}, 20] (* Harvey P. Dale, Apr 01 2020 *)

CROSSREFS

Cf. A195878, A161852.

Sequence in context: A293050 A052581 A052605 * A334189 A042120 A002980

Adjacent sequences:  A195914 A195915 A195916 * A195918 A195919 A195920

KEYWORD

nonn,easy

AUTHOR

Sture Sjöstedt, Oct 26 2011

EXTENSIONS

More terms from Bruno Berselli, Oct 28 2011

STATUS

approved

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Last modified May 6 17:59 EDT 2021. Contains 343586 sequences. (Running on oeis4.)