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A254138 Pentagonal numbers (A000326) which are also centered hexagonal numbers (A003215). 3
1, 7957, 1185037, 10596309577, 1578130224697, 14111253811878301, 2101618114050816901, 18792154258821103289617, 2798754265133491448134897, 25025774916617575492416996517, 3727140237435880812247465267837, 33327174817289665775049786996211801 (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+7956*x^3-154634*x^2+7956*x+1) / ((x-1)*(x^2-1154*x+1)*(x^2+1154*x+1)).

EXAMPLE

7957 is in the sequence because it is the 73rd pentagonal number and the 52nd centered hexagonal number.

PROG

(PARI) Vec(-x*(x^4+7956*x^3-154634*x^2+7956*x+1)/((x-1)*(x^2-1154*x+1)*(x^2+1154*x+1)) + O(x^100))

CROSSREFS

Cf. A000326, A003215, A254136, A254137.

Sequence in context: A316907 A293623 A316908 * A157660 A236786 A252190

Adjacent sequences:  A254135 A254136 A254137 * A254139 A254140 A254141

KEYWORD

nonn,easy

AUTHOR

Colin Barker, Jan 26 2015

STATUS

approved

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Last modified January 27 08:21 EST 2022. Contains 350606 sequences. (Running on oeis4.)