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A273367 Numbers k such that 10*k+6 is a perfect square. 5
1, 3, 19, 25, 57, 67, 115, 129, 193, 211, 291, 313, 409, 435, 547, 577, 705, 739, 883, 921, 1081, 1123, 1299, 1345, 1537, 1587, 1795, 1849, 2073, 2131, 2371, 2433, 2689, 2755, 3027, 3097, 3385, 3459, 3763, 3841, 4161, 4243, 4579 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (1, 2, -2, -1, 1).

FORMULA

a(2n) = 10*n^2 - 8*n + 1.

a(2n+1) = 10*n^2 + 8*n + 1.

G.f.: (x^4+2x^3+14x^2+2x+1)/((1-x)^3*(1+x)^2).

a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5). - G. C. Greubel, May 20 2016

MATHEMATICA

LinearRecurrence[{1, 2, -2, -1, 1}, {1, 3, 19, 25, 57}, 50] (* G. C. Greubel, May 20 2016 *)

PROG

(PARI) is(n)=issquare(10*n+6) \\ Charles R Greathouse IV, Jan 31 2017

CROSSREFS

Cf. A132356, A273365, A273366, A273368.

Cf. A033583 (perfect squares ending in 0 in base 10 with final 0 removed).

Sequence in context: A323784 A063557 A197541 * A295322 A296934 A062619

Adjacent sequences:  A273364 A273365 A273366 * A273368 A273369 A273370

KEYWORD

nonn,easy

AUTHOR

Nathan Fox, Brooke Logan, and N. J. A. Sloane, May 20 2016

STATUS

approved

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Last modified April 23 18:28 EDT 2019. Contains 322387 sequences. (Running on oeis4.)