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A120390
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Sum of digits of double factorial numbers.
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6
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1, 2, 3, 8, 6, 12, 6, 15, 18, 15, 18, 18, 18, 18, 18, 18, 36, 45, 45, 36, 45, 45, 36, 54, 63, 45, 72, 45, 72, 72, 90, 90, 90, 81, 108, 81, 108, 81, 126, 90, 108, 108, 144, 81, 144, 90, 135, 117, 144, 126, 153, 108, 180, 135, 180, 135, 171, 180, 180, 171, 198, 180, 198
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OFFSET
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1,2
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COMMENTS
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If n > 10, then 9 divides a(n). - Michel Lagneau, Dec 22 2011
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..1000
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FORMULA
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a(n) = A007953(A006882(n)) - Eric Chen, Jun 13 2018
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EXAMPLE
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5!! = 5*3*1 = 15 --> 1+5 = 6
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MAPLE
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P:=proc(n) local i, j, k, t1, t2; for i from 1 by 1 to n do j:=i; k:=i-2; while k>0 do j:=j*k; k:=k-2; od; t1:=j; t2:=0; while t1 <> 0 do t2:= t2+(t1 mod 10); t1 := floor(t1/10); od; print(t2); od; end: P(100);
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MATHEMATICA
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Table[Total[IntegerDigits[n!!]], {n, 70}] (* Harvey P. Dale, May 19 2021 *)
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CROSSREFS
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Cf. A004152, A006882, A007953.
Sequence in context: A160582 A321668 A112977 * A109230 A262992 A036970
Adjacent sequences: A120387 A120388 A120389 * A120391 A120392 A120393
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KEYWORD
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easy,nonn,base
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AUTHOR
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Paolo P. Lava and Giorgio Balzarotti, Jun 30 2006
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STATUS
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approved
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