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Search: id:A130318
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| A130318 |
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Integer values of n!!/S(n), where S(n) is the sum of all odd numbers minor or equal to n, if n is odd, or the sum of all even numbers minor or equal to n, if n is even. |
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+0
3
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| 1, 1, 4, 128, 11520, 143360, 425425, 2064384, 619315200, 280284364800, 6801567252480, 27512370460575, 178541140377600, 152355106455552000, 167834385271436083200, 6074006324109115392000, 29734853645550994565625
(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 eighth term all the numbers end for 0 or 5.
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FORMULA
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Integer of the form n!!/A005408, for n odd and n!!/A002378 (offset 2) for n even.
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EXAMPLE
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6 --> 6!! = 48; 6 + 4 + 2 = 12; 48/12 = 4.
17 --> 17!! = 34459425; 17 + 15 + 13 + 11 + 9 + 7 + 5 + 3 + 1 = 81; 34459425/81 = 425425.
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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:=i; w:=i-2; while w>0 do j:=j+w; w:=w-2; od; 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. A108552, A000290, A005408, A130319.
Sequence in context: A152421 A128790 A013823 this_sequence A000318 A141367 A141368
Adjacent sequences: A130315 A130316 A130317 this_sequence A130319 A130320 A130321
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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 23 2007
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