A273054 Numbers n such that 19*n^2 + 20 is a square.

4, 22, 1382, 7484, 469876, 2544538, 159756458, 865135436, 54316725844, 294143503702, 18467527030502, 100007926123244, 6278904873644836, 34002400738399258, 2134809189512213738, 11560716243129624476, 725828845529279026084, 3930609520263333922582

Offset

1,1

Links

Colin Barker, Table of n, a(n) for n = 1..750

Index entries for linear recurrences with constant coefficients, signature (0,340,0,-1).

Formula

G.f.: 2*x*(2 + 11*x + 11*x^2 + 2*x^3)/(1 - 340*x^2 + x^4).

a(n) = 340*a(n-2) - a(n-4), for n>3.

Mathematica

LinearRecurrence[{0, 340, 0, -1}, {4, 22, 1382, 7484}, 30]

Prog

(Magma) I:=[4, 22, 1382, 7484]; [n le 4 select I[n] else 340*Self(n-2)-Self(n-4): n in [1..30]];
(PARI) x='x+O('x^99); Vec(2*x*(2+11*x+11*x^2+2*x^3)/(1-340*x^2+x^4)) \\ Altug Alkan, May 14 2016

Crossrefs

Cf. similar sequences listed in A273052.

Sequence in context: A104166 A362823 A368140 * A065401 A053775 A037142

Adjacent sequences: A273051 A273052 A273053 * A273055 A273056 A273057

Keyword

nonn,easy

Author

Vincenzo Librandi, May 14 2016

Status

approved