A131091 - OEIS

A131091

Partial sums of A131707.

1, 2, 5, 12, 19, 20, 29, 38, 45, 48, 51, 60, 61, 62, 65, 72, 79, 80, 89, 98, 105, 108, 111, 120, 121, 122, 125, 132, 139, 140, 149, 158, 165, 168, 171, 180, 181, 182, 185, 192, 199, 200, 209, 218, 225, 228, 231, 240, 241, 242, 245, 252, 259, 260, 269, 278, 285

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OFFSET

0,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,-1,2,-1).

FORMULA

a(n) = Sum_{i=0..n} A131707(i), where A131707(n) = A001333(n) mod 10.

O.g.f.: (9x^6-6x^5+4x^3+2x^2+1)/((x-1)^2*(x^2+1)*(x^4-x^2+1)). - R. J. Mathar, Jul 16 2008

a(n) = 2*a(n-1) - a(n-2) - a(n-6) + 2*a(n-7) - a(n-8) for n > 7. - Chai Wah Wu, Jan 09 2021

MATHEMATICA

Accumulate[PadRight[{}, 60, {1, 1, 3, 7, 7, 1, 9, 9, 7, 3, 3, 9}]] (* Harvey P. Dale, Jul 30 2025 *)