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A253823 Octagonal numbers (A000567) which are also centered triangular numbers (A005448). 3
1, 97921, 1039585, 130402572385, 1384429704481, 173658931280825761, 1843664419471976641, 231264030011583194717761, 2455233718711319470593985, 307977546462671843639087352385, 3269669116478082433043125969441, 410138010309759307549971991199125921 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Colin Barker, Table of n, a(n) for n = 1..327

Index entries for linear recurrences with constant coefficients, signature (1,1331714,-1331714,-1,1).

FORMULA

a(n) = a(n-1)+1331714*a(n-2)-1331714*a(n-3)-a(n-4)+a(n-5).

G.f.: -x*(x^4+97920*x^3-390050*x^2+97920*x+1) / ((x-1)*(x^2-1154*x+1)*(x^2+1154*x+1)).

EXAMPLE

97921 is in the sequence because it is the 181st octagonal number and the 256th centered triangular number.

PROG

(PARI) Vec(-x*(x^4+97920*x^3-390050*x^2+97920*x+1)/((x-1)*(x^2-1154*x+1)*(x^2+1154*x+1)) + O(x^100))

CROSSREFS

Cf. A000567, A005448, A253821, A253822.

Sequence in context: A022214 A237509 A109185 * A316488 A235196 A002273

Adjacent sequences:  A253820 A253821 A253822 * A253824 A253825 A253826

KEYWORD

nonn,easy

AUTHOR

Colin Barker, Jan 14 2015

STATUS

approved

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Last modified July 6 23:01 EDT 2020. Contains 335484 sequences. (Running on oeis4.)