%I #12 Nov 08 2018 11:09:23

%S 1,3,19,25,57,67,115,129,193,211,291,313,409,435,547,577,705,739,883,

%T 921,1081,1123,1299,1345,1537,1587,1795,1849,2073,2131,2371,2433,2689,

%U 2755,3027,3097,3385,3459,3763,3841,4161,4243,4579

%N Numbers k such that 10*k+6 is a perfect square.

%H G. C. Greubel, <a href="/A273367/b273367.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1, 2, -2, -1, 1).

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

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

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

%F 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

%t LinearRecurrence[{1, 2, -2, -1, 1}, {1, 3, 19, 25, 57}, 50] (* _G. C. Greubel_, May 20 2016 *)

%o (PARI) is(n)=issquare(10*n+6) \\ _Charles R Greathouse IV_, Jan 31 2017

%Y Cf. A132356, A273365, A273366, A273368.

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

%K nonn,easy

%O 0,2

%A _Nathan Fox_, _Brooke Logan_, and _N. J. A. Sloane_, May 20 2016