OFFSET
17,1
COMMENTS
If X is a previous term of the sequence greater than zero and less than 10, then PD=X and SD=X and so the next term is 2X.
The values of a(n) for n = 1..12 are 19, 34, 46, 177, 458, 2699, 279999, 4557888, 23366667799, 456667788889999, 246666666666666667888999, and 23777777777777777888888888899999999. - Giovanni Resta, Jan 02 2014
EXAMPLE
For n=18: 1, 2, 4, 8, 16, 13, 7, 14, 9, 18, 17, 15, 11, 3, 6, 12, 5, 10.
For n=19: 26, 20, 4, 8, 16, 13, 7, 14, 9, 18, 17, 15, 11, 3, 6, 12, 5, 10, 2.
PROG
(PARI) step(n)=my(d=digits(n), D=select(k->k>1, d)); sum(i=1, #d, d[i]) + prod(i=1, #D, D[i])
len(n)=my(v=Set([n])); while(1, n=step(n); if(setsearch(v, n), return(#v)); v=setunion(v, Set([n])))
a(n)=my(k); while(len(k++)!=n, ); k \\ Charles R Greathouse IV, Jan 02 2014
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Carlos Rivera, Jan 02 2014
EXTENSIONS
a(17) and a(27)-a(30) from Giovanni Resta, Jan 02 2014
STATUS
approved