login
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
OFFSET
1,2
COMMENTS
If n > 10, then 9 divides a(n). - Michel Lagneau, Dec 22 2011
LINKS
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
KEYWORD
easy,nonn,base
AUTHOR
STATUS
approved