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Search: id:A130332
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| A130332 |
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Integer values of n!!/sum(i=0..n,n), with n>=1. |
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+0
2
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| 1, 1, 21, 1485, 6144, 225225, 17694720, 59520825, 6539968512, 24325703325, 145332633600, 14230536445125, 2596962041856000, 11288163762500625, 78354054748569600, 11665426077721040625, 86068915523813376000
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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After the ninth term all the other numbers end in 0 or 5.
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EXAMPLE
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5!! = 5*3*1 = 15; 5+4+3+2+1 = 15; 15/15 = 1.
13!! = 13*11*9*7*5*3*1 = 135135; 13+12+11+10+9+8+7+6+5+4+3+2+1 = 91; 135135/91 = 1485.
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MAPLE
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P:=proc(n) local a, i, j, k, w; for i from 1 by 1 to n do k:=i; w:=i-2; while w>0 do k:=k*w; w:=w-2; od; j:=sum('w', 'w'=1..i); a:=k/j; if trunc(a)=a then print(a) fi; od; end: P(100);
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CROSSREFS
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Cf. A130318, A126695, A108552.
Sequence in context: A036059 A036519 A118446 this_sequence A035319 A081786 A130039
Adjacent sequences: A130329 A130330 A130331 this_sequence A130333 A130334 A130335
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KEYWORD
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easy,nonn
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AUTHOR
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Paolo P. Lava & Giorgio Balzarotti (ppl(AT)spl.at), May 24 2007
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