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A254966
Heptagonal numbers (A000566) that are also centered hexagonal numbers (A003215).
3
1, 7, 469, 3367, 226051, 1622881, 108956107, 782225269, 52516617517, 377030956771, 25312900687081, 181728138938347, 12200765614555519, 87592585937326477, 5880743713315073071, 42219444693652423561, 2834506269052250664697, 20349684749754530829919
OFFSET
1,2
FORMULA
a(n) = a(n-1)+482*a(n-2)-482*a(n-3)-a(n-4)+a(n-5).
G.f.: -x*(x^4+6*x^3-20*x^2+6*x+1) / ((x-1)*(x^2-22*x+1)*(x^2+22*x+1)).
EXAMPLE
469 is in the sequence because it is the 14th heptagonal number and the 13th centered hexagonal number.
MATHEMATICA
LinearRecurrence[{1, 482, -482, -1, 1}, {1, 7, 469, 3367, 226051}, 20] (* Harvey P. Dale, May 17 2019 *)
PROG
(PARI) Vec(-x*(x^4+6*x^3-20*x^2+6*x+1)/((x-1)*(x^2-22*x+1)*(x^2+22*x+1)) + O(x^100))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Feb 11 2015
STATUS
approved