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A249349
(A001147(n+1)-1)/2, equals the index of A249348(n) within the triangular numbers A000217.
2
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.
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
KEYWORD
nonn
AUTHOR
M. F. Hasler, Oct 26 2014
STATUS
approved