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A113588 a(1) = 3, a(n+1) = d!, where d is the sum of decimal digits of a(n). 2
3, 6, 720, 362880, 10888869450418352160768000000 (list; graph; refs; listen; history; text; internal format)
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

LINKS

Table of n, a(n) for n=1..5.

FORMULA

a(n+1) = A000142(A007953(a(n))).- M. F. Hasler, Mar 15 2016

EXAMPLE

a(2) = 6, a(3) = 6! = 720, a(4)= (7+2+0)! = 9! = 362880. a(5) = 27!

MAPLE

A007953 := proc(n) add(i, i= convert(n, base, 10)) ; end: A113588 := proc(n) option remember ; if n = 1 then 3; else factorial(A007953(A113588(n-1)) ) ; fi; end: for n from 1 to 6 do printf("%d, ", A113588(n)) ; od: # R. J. Mathar, Feb 06 2008

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

Sequence in context: A179267 A171928 A034879 * A071106 A157548 A134901

Adjacent sequences:  A113585 A113586 A113587 * A113589 A113590 A113591

KEYWORD

nonn,base,easy

AUTHOR

Amarnath Murthy, Nov 07 2005

EXTENSIONS

More terms from R. J. Mathar, Feb 06 2008

STATUS

approved

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Last modified June 17 21:47 EDT 2019. Contains 324200 sequences. (Running on oeis4.)