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

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