A111300 Positive integers that are the difference between two double factorials.

0, 1, 2, 5, 6, 7, 12, 13, 14, 33, 40, 45, 46, 47, 57, 90, 97, 102, 103, 104, 279, 336, 369, 376, 381, 382, 383, 561, 840, 897, 930, 937, 942, 943, 944, 2895, 3456, 3735, 3792, 3825, 3832, 3837, 3838, 3839, 6555, 9450, 10011, 10290, 10347, 10380, 10387, 10392

Offset: 1

Author

Paolo P. Lava and Giorgio Balzarotti, Nov 02 2005

Keywords

• easy
• nonn

Examples

			7!! - 4!! = 7*5*3*1 - 4*2 = 105 - 8 = 97.
9!! - 5!! = 9*7*5*3*1 - 5*3*1 = 945 - 15 = 930.
		

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A006882 (n!!).

Programs

Mathematica

terms[n_]:=Sort[Union[Flatten[Table[j!!-i!!,{i,n},{j,i,n}]]]]; terms[12] (* Enrique Pérez Herrero, May 21 2011 *)

Formula

M!! - N!! where M and N positive integers.

Extensions

Extended by T. D. Noe, May 22 2011