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A120390 Sum of digits of double factorial numbers. 6
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

If n > 10, then 9 divides a(n). - Michel Lagneau, Dec 22 2011

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A007953(A006882(n)) - Eric Chen, Jun 13 2018

EXAMPLE

5!! = 5*3*1 = 15 --> 1+5 = 6

MAPLE

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);

MATHEMATICA

Table[Total[IntegerDigits[n!!]], {n, 70}] (* Harvey P. Dale, May 19 2021 *)

CROSSREFS

Cf. A004152, A006882, A007953.

Sequence in context: A160582 A321668 A112977 * A109230 A262992 A036970

Adjacent sequences:  A120387 A120388 A120389 * A120391 A120392 A120393

KEYWORD

easy,nonn,base

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, Jun 30 2006

STATUS

approved

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Last modified May 29 04:32 EDT 2022. Contains 354122 sequences. (Running on oeis4.)