|
%I #12 Jan 03 2016 15:00:13
%S 1,2,4,9,14,16,12,34,52,90,60,66,54,42,30,126,114,102,624,760,680,580,
%T 540,748,740,520,672,408,666,360,264,546,510,330,318,2960,2574,1782,
%U 1494,3672,3114,2790,1680,1386,1374,930,612,594,582,378,366,180,3570
%N Smallest number that takes n steps to get to 1 under the map f(n)=sigma(n)-n, the sum of the proper divisors.
%H T. D. Noe, <a href="/A059447/b059447.txt">Table of n, a(n) for n = 0..150</a>
%e a(4)=14 since 14->10->8->7->1 and no smaller number takes 4 steps.
%t f[n_] := DivisorSigma[1, n] - n; f[1] = 1; a[n_] := Catch[For[k = 1, True, k++, nl = NestList[f, k, n]; p = Position[nl, 1, 1, 1]; If[p != {}, If[p[[1, 1]] - 1 == n, Throw[k]]]]]; Table[a[n], {n, 0, 52}] (* _Jean-François Alcover_, Feb 01 2013 *)
%Y Cf. A003023 (length of aliquot sequence for n).
%K nice,nonn
%O 0,2
%A _Erich Friedman_, Feb 02 2001
%E More terms from _T. D. Noe_, Nov 27 2006
|
