

A253880


Triangular numbers (A000217) that are also centered heptagonal numbers (A069099).


6



1, 253, 64261, 16322041, 4145734153, 1053000152821, 267457893082381, 67933251842771953, 17254778510170993681, 4382645808331589623021, 1113174780537713593253653, 282742011610770921096804841, 71815357774355276244995175961, 18240818132674629395307677889253
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OFFSET

1,2


LINKS

Colin Barker, Table of n, a(n) for n = 1..416
Index entries for linear recurrences with constant coefficients, signature (254,1).


FORMULA

a(n) = 254*a(n1)  a(n2).
G.f.: x*(x1) / (x^2  254*x + 1).


EXAMPLE

253 is in the sequence because it is the 22nd triangular number and the 9th centered heptagonal number.


MATHEMATICA

LinearRecurrence[{254, 1}, {1, 253}, 20] (* Harvey P. Dale, May 17 2017 *)


PROG

(PARI) Vec(x*(x1)/(x^2254*x+1) + O(x^100))


CROSSREFS

Cf. A000217, A069099, A253878, A253879.
Similar sequences of the type cosh((2*m+1)*arccosh(k))/k are listed in A302329. This is the case k=8.
Sequence in context: A176087 A006060 A077695 * A145628 A237419 A243666
Adjacent sequences: A253877 A253878 A253879 * A253881 A253882 A253883


KEYWORD

nonn,easy


AUTHOR

Colin Barker, Jan 17 2015


STATUS

approved



