OFFSET
1,1
COMMENTS
The next term, a(6) = 108!, has 175 digits. - If one omits to take the sum of the digits, i.e., a(n+1)=a(n)!, where a(1)=3 is the least starting value that does not lead to a constant sequence, then the first three terms are the same but a(4) has 1747 digits. - M. F. Hasler, Mar 15 2016
FORMULA
EXAMPLE
a(2) = 6;
a(3) = 6! = 720;
a(4) = (7+2+0)! = 9! = 362880;
a(5) = 27!.
MAPLE
MATHEMATICA
NestList[Factorial@ Total[IntegerDigits@ #] &, 3, 4] (* Michael De Vlieger, Mar 15 2016 *)
PROG
(PARI) A007953(n, a=3)={for(i=2, n, a=sumdigits(a)!); a} \\ M. F. Hasler, Mar 15 2016
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Amarnath Murthy, Nov 07 2005
EXTENSIONS
More terms from R. J. Mathar, Feb 06 2008
STATUS
approved