The OEIS is supported by the many generous donors to the OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A337789 Numbers k such that trajectory of k under repeated calculation of fecundity (x -> A070562(x))  eventually reaches 0. 1
 0, 1, 5, 10, 15, 18, 20, 21, 22, 24, 27, 30, 35, 40, 42, 44, 46, 48, 50, 51, 55, 59, 60, 63, 64, 66, 67, 69, 70, 74, 75, 77, 80, 83, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 115, 118, 120, 121, 122, 124, 127 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE 5 is a term in the sequence because the fecundity of 5 is 1, the fecundity of 1 is 10 and the fecundity of 10 is 0. 7 is not a term in the sequence because the fecundity of 7 is 7 and therefore the fecundity will never become 0. MAPLE fec:= proc(n) local k, x, t;   x:= n;   for k from 0 do     t:= convert(convert(x, base, 10), `*`);     if t = 0 then return k fi;     x:= x+t   od end proc: filter:= proc(n) local v; option remember;     v:= fec(n);     if v = 0 then true     elif v = n then false     else procname(v)     fi end proc: select(filter, [\$0..1000]); # Robert Israel, Apr 12 2021 MATHEMATICA fec[n_] := Length @ FixedPointList[# + Times @@ IntegerDigits[#] &, n] - 2; Select[Range[0, 100], FixedPoint[fec, #] == 0 &] (* Amiram Eldar, Sep 22 2020 *) PROG (Python) from math import prod from functools import lru_cache def pd(n): return prod(map(int, str(n))) def A070562(n):   s = 0   while pd(n) != 0: n, s = n + pd(n), s + 1   return s @lru_cache(maxsize=None) def ok(n):   fn = A070562(n)   if fn == 0: return True   if fn == n: return False   return ok(fn) print(list(filter(ok, range(128)))) # Michael S. Branicky, Apr 12 2021 CROSSREFS Cf. A070562, A070061, A070257. Sequence in context: A313672 A313673 A313674 * A282145 A313675 A313676 Adjacent sequences:  A337786 A337787 A337788 * A337790 A337791 A337792 KEYWORD nonn,easy,base AUTHOR Robert Bilinski, Sep 21 2020 EXTENSIONS More terms from Amiram Eldar, Sep 22 2020 Offset changed by Robert Israel, Apr 12 2021 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 29 17:18 EDT 2022. Contains 357090 sequences. (Running on oeis4.)