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A059447 Smallest number that takes n steps to get to 1 under the map f(n)=sigma(n)-n, the sum of the proper divisors. 2
1, 2, 4, 9, 14, 16, 12, 34, 52, 90, 60, 66, 54, 42, 30, 126, 114, 102, 624, 760, 680, 580, 540, 748, 740, 520, 672, 408, 666, 360, 264, 546, 510, 330, 318, 2960, 2574, 1782, 1494, 3672, 3114, 2790, 1680, 1386, 1374, 930, 612, 594, 582, 378, 366, 180, 3570 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

T. D. Noe, Table of n, a(n) for n = 0..150

EXAMPLE

a(4)=14 since 14->10->8->7->1 and no smaller number takes 4 steps.

MATHEMATICA

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-Fran├žois Alcover, Feb 01 2013 *)

CROSSREFS

Cf. A003023 (length of aliquot sequence for n).

Sequence in context: A090942 A085901 A077224 * A234899 A190553 A270532

Adjacent sequences:  A059444 A059445 A059446 * A059448 A059449 A059450

KEYWORD

nice,nonn

AUTHOR

Erich Friedman, Feb 02 2001

EXTENSIONS

More terms from T. D. Noe, Nov 27 2006

STATUS

approved

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Last modified December 10 21:23 EST 2016. Contains 279011 sequences.