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A259403
Pentagonal numbers (A000326) that are the sum of eleven consecutive pentagonal numbers.
5
2882, 27676, 1114135, 10982301, 443390277, 4370895551, 176468183540, 1739605414426, 70233893626072, 692358584013426, 27952913194960545, 275556976831896551, 11125189217700638267, 109670984420510781301, 4427797355731659037150, 43648776242386459028676
OFFSET
1,1
FORMULA
G.f.: -11*x*(16*x^4+14*x^3-5507*x^2+2254*x+262) / ((x-1)*(x^2-20*x+1)*(x^2+20*x+1)).
EXAMPLE
2882 is in the sequence because P(44) = 2882 = 92 + 117 + 145 + 176 + 210 + 247 + 287 + 330 + 376 + 425 + 477 = P(8)+ ... +P(18).
MATHEMATICA
LinearRecurrence[{1, 398, -398, -1, 1}, {2882, 27676, 1114135, 10982301, 443390277}, 30] (* Harvey P. Dale, Jan 21 2017 *)
PROG
(PARI) Vec(-11*x*(16*x^4+14*x^3-5507*x^2+2254*x+262)/((x-1)*(x^2-20*x+1)*(x^2+20*x+1)) + O(x^20))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jun 26 2015
STATUS
approved