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A106390 Numbers k such that 13k = 6j^2 + 6j + 1. 3
1, 61, 97, 277, 349, 649, 757, 1177, 1321, 1861, 2041, 2701, 2917, 3697, 3949, 4849, 5137, 6157, 6481, 7621, 7981, 9241, 9637, 11017, 11449, 12949, 13417, 15037, 15541, 17281, 17821, 19681, 20257, 22237, 22849, 24949, 25597, 27817, 28501, 30841 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..40.

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

FORMULA

a(1)=1, a(2)=61; for odd n a(n) = a(n-1)+18*(n-1), for even n a(n) = a(n-1)+60*(n-1).

a(n) = (25-21*(-1)^n+6*(-13+7*(-1)^n)*n+78*n^2)/4. - Colin Barker, Apr 16 2014

G.f.: -x*(x^4+60*x^3+34*x^2+60*x+1) / ((x-1)^3*(x+1)^2). - Colin Barker, Apr 16 2014

MATHEMATICA

f[n_] := Block[{k = (6n(n + 1) + 1)/13}, If[ IntegerQ[k], k, 1]]; Union[ Table[ f[n], {n, 270}]] (* Robert G. Wilson v, May 02 2005 *)

PROG

(PARI) Vec(-x*(x^4+60*x^3+34*x^2+60*x+1)/((x-1)^3*(x+1)^2) + O(x^100)) \\ Colin Barker, Apr 16 2014

CROSSREFS

Cf. A106387, A106388, A106389.

For j sequence see A106389.

Sequence in context: A020350 A142108 A033239 * A142191 A086126 A023287

Adjacent sequences:  A106387 A106388 A106389 * A106391 A106392 A106393

KEYWORD

nonn,easy

AUTHOR

Pierre CAMI, May 01 2005

EXTENSIONS

More terms from Robert G. Wilson v, May 02 2005

STATUS

approved

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Last modified July 19 11:12 EDT 2019. Contains 325158 sequences. (Running on oeis4.)