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A106388
Numbers k such that 11k = 6j^2 + 6j + 1.
4
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
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
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