A249349 - OEIS

A249349

(A001147(n+1)-1)/2, equals the index of A249348(n) within the triangular numbers A000217.

0, 1, 7, 52, 472, 5197, 67567, 1013512, 17229712, 327364537, 6874655287, 158117071612, 3952926790312, 106729023338437, 3095141676814687, 95949391981255312, 3166329935381425312, 110821547738349885937, 4100397266318945779687, 159915493386438885407812

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OFFSET

0,3

COMMENTS

Also a(n) = floor(sqrt(A249348(n)*2)).

The positive terms are of the form 3k-2; this k (= 1, 3, 18, 157, ...) is the index of A249348(n) within the centered 9-gonal numbers A060544.

LINKS

Table of n, a(n) for n=0..19.

FORMULA

a(n) +(-2*n-3)*a(n-1) +(4*n-1)*a(n-2) +(-2*n+3)*a(n-3)=0. - R. J. Mathar, Oct 28 2014

PROG

(PARI) a(n)=A001147(n+1)\2

(PARI) vector(10, n, A001147(n)\2) \\ To get the initial term a(0) for n=1.

CROSSREFS

Sequence in context: A162233 A185623 A193881 * A300492 A179517 A300932

Adjacent sequences: A249346 A249347 A249348 * A249350 A249351 A249352

KEYWORD

nonn

AUTHOR

M. F. Hasler, Oct 26 2014

STATUS

approved