A106388 Numbers k such that 11k = 6j^2 + 6j + 1.

11, 23, 131, 167, 383, 443, 767, 851, 1283, 1391, 1931, 2063, 2711, 2867, 3623, 3803, 4667, 4871, 5843, 6071, 7151, 7403, 8591, 8867, 10163, 10463, 11867, 12191, 13703, 14051, 15671, 16043, 17771, 18167, 20003, 20423, 22367, 22811, 24863, 25331, 27491, 27983

Offset

1,1

Comments

j sequence = A106387

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

Formula

a(1)=11, a(2)=23; if n odd a(n)=a(n-1)+54*(n-1), if n even a(n)=a(n-1)+12*(n-1).

a(n) = (66*n*(n-1)-21*(2*n-1)*(-1)^n+23)/4.

G.f.: x*(11+12*x+86*x^2+12*x^3+11*x^4)/((1+x)^2*(1-x)^3).

a(n)-a(n-1)-2*a(n-2)+2*a(n-3)+a(n-4)-a(n-5) = 0 for n>5.

Mathematica

LinearRecurrence[{1, 2, -2, -1, 1}, {11, 23, 131, 167, 383}, 50] (* Harvey P. Dale, Jul 26 2018 *)

Prog

(PARI) Vec((11+12*x+86*x^2+12*x^3+11*x^4)/(1+x)^2/(1-x)^3+O(x^99)) \\ Charles R Greathouse IV, Dec 28 2011

Crossrefs

Cf. A106387, A106389, A106390.

Sequence in context: A288406 A014874 A027899 * A171068 A091465 A261352

Adjacent sequences: A106385 A106386 A106387 * A106389 A106390 A106391

Keyword

nonn,easy

Author

Pierre CAMI, May 01 2005

Extensions

Formulae corrected and added by Bruno Berselli, Nov 16 2010

More terms from Colin Barker, Apr 16 2014

Status

approved