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A073013 (1/2)*sum(k=1,n,(n+k)!/(k!)^2). 0
1, 6, 37, 255, 1991, 17598, 174924, 1937715, 23696029, 317105778, 4608337064, 72249308222, 1215116713110, 21816229444012, 416367513788760, 8415762294812355, 179556294350582865, 4032049130587198650 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) is odd for n = 1,3 and if n is of the form 2^m or 2^m+1 (with m>= 2) (i.e. a(n) is odd if n=1,3,4,5,8,9,16,17,32,33,64,65,128,129,256,257...)

LINKS

Table of n, a(n) for n=1..18.

PROG

(PARI) a(n)=if(n<0, 0, sum(k=1, n, (n+k)!/(k!)^2)/2)

CROSSREFS

Sequence in context: A005389 A080954 A271905 * A192238 A140712 A079751

Adjacent sequences:  A073010 A073011 A073012 * A073014 A073015 A073016

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Aug 03 2002

STATUS

approved

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Last modified June 22 16:01 EDT 2021. Contains 345386 sequences. (Running on oeis4.)