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Search: id:A130333
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| A130333 |
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Numbers n for which n!!/sum(i=0..n,n), with n>=1, is an integer. |
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+0
1
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| 1, 5, 9, 13, 14, 17, 20, 21, 24, 25, 26, 29, 32, 33, 34, 37, 38, 41, 44, 45, 48, 49, 50, 53, 54, 56, 57, 61, 62, 64, 65, 68, 69, 73, 74, 76, 77, 80, 81, 84, 85, 86, 89, 90, 92, 93, 94, 97, 98
(list; graph; listen)
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OFFSET
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0,2
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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(i) fi; od; end: P(100);
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CROSSREFS
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Cf. A130319, A130332.
Adjacent sequences: A130330 A130331 A130332 this_sequence A130334 A130335 A130336
Sequence in context: A079357 A080455 A122798 this_sequence A080579 A062976 A080580
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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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