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Search: id:A073013
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| A073013 |
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(1/2)*sum(k=1,n,(n+k)!/(k!)^2). |
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+0
1
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| 1, 6, 37, 255, 1991, 17598, 174924, 1937715, 23696029, 317105778, 4608337064, 72249308222, 1215116713110, 21816229444012, 416367513788760, 8415762294812355, 179556294350582865, 4032049130587198650
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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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...)
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PROGRAM
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(PARI) a(n)=if(n<0, 0, sum(k=1, n, (n+k)!/(k!)^2)/2)
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CROSSREFS
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Sequence in context: A081188 A005389 A080954 this_sequence A140712 A079751 A088312
Adjacent sequences: A073010 A073011 A073012 this_sequence A073014 A073015 A073016
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 03 2002
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