|
| |
|
|
A130333
|
|
Numbers n for which n!!/sum(i=0..n,n), with n>=1, is an integer.
|
|
0
| |
|
|
1, 5, 9, 13, 14, 17, 20, 21, 24, 25, 26, 29, 32, 33, 34, 37, 38, 41, 44, 45, 48, 49, 50, 53, 54, 56, 57, 61, 62, 64, 65, 68, 69, 73, 74, 76, 77, 80, 81, 84, 85, 86, 89, 90, 92, 93, 94, 97, 98
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 0,2
|
|
|
EXAMPLE
| 5!! = 5*3*1 = 15; 5+4+3+2+1 = 15; 15/15 = 1.
13!! = 13*11*9*7*5*3*1 = 135135; 13+12+11+10+9+8+7+6+5+4+3+2+1 = 91; 135135/91 = 1485.
|
|
|
MAPLE
| 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:=sum('w', 'w'=1..i); a:=k/j; if trunc(a)=a then print(i) fi; od; end: P(100);
|
|
|
CROSSREFS
| Cf. A130319, A130332.
Sequence in context: A080455 A122798 A189464 * A080579 A165971 A160522
Adjacent sequences: A130330 A130331 A130332 * A130334 A130335 A130336
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| Paolo P. Lava & Giorgio Balzarotti (paoloplava(AT)gmail.com), May 24 2007
|
| |
|
|
