A033945 -id:A033945 - cp's OEIS frontend

A033946 Values of n corresponding to A033945.

1, 2, 3, 5, 7, 9, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263

Offset: 1

N. J. A. Sloane

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A033885, A033945.

f[n_] := 3n - DivisorSigma[1, n]; fm = 0; s = {}; Do[f1 = f[n]; If[f1 > fm, fm = f1; AppendTo[s, n]], {n, 1, 263}]; s (* Amiram Eldar, Aug 28 2019 *)

More terms from Asher Auel May 05 2000

A037159 Consider the trajectory of n under the iteration of a map which sends x to 3x - sigma(x) if this is >= 0; otherwise the iteration stops. The sequence gives values of n which eventually reach 0.

Original entry on oeis.org

82, 120, 280, 672, 1464, 3048, 4964, 5568, 5688, 7666, 8969, 9176, 9288, 9514, 9616, 9706, 10132, 10186, 10232, 10478, 11496, 11884, 11914, 12232, 12320, 12820, 13248, 13842, 13854, 13866, 14848, 15076, 15098, 15196, 15364, 15586, 15892

Offset: 1

Naohiro Nomoto

A perfect number is a fixed point of this map.

			82 -> 120 -> 0.

To see why 1, 16 and 23 are not in the sequence, see A058541, A058542 and A058545.

Cf. A033885, A033945, A033946, A037160.

max = 16000; f[0] = 0; f[n_ /; 0 < n < 9max] := 3n - DivisorSigma[1, n]; f[] = -1; Select[ Range[max], FixedPoint[f, #] == 0 &] (* _Jean-François Alcover, Feb 22 2012 *)

Better description from Jud McCranie, Dec 24 2000

Definition clarified by Harvey P. Dale, Jul 30 2020

cp's OEIS Frontend

A033946 Values of n corresponding to A033945.

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