A120390 Sum of digits of double factorial numbers.

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

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