A159953 Values in A054973 larger than 1.

2, 2, 3, 2, 2, 3, 3, 2, 2, 3, 5, 2, 3, 3, 4, 2, 2, 2, 2, 4, 2, 2, 2, 2, 2, 5, 2, 2, 6, 4, 2, 2, 5, 2, 5, 3, 3, 3, 7, 3, 6, 2, 3, 2, 2, 6, 3, 2, 4, 2, 3, 8, 2, 9, 4, 2, 6, 2, 2, 2, 2, 2, 2, 4, 8, 4, 2, 2, 2, 3, 4, 3, 9, 2, 10, 2, 3, 2, 4, 4, 3, 4, 2, 2, 11, 5, 2, 5, 2, 3, 4, 2, 2, 3, 5, 3, 8, 7, 4, 15, 2, 4, 7, 8

Offset: 1

Author

Jaroslav Krizek, Apr 27 2009

Keywords

• nonn

Comments

This is a survey of how many solutions the equation sigma(x)=k has for k in A159886, or about the lengths of the plateaus in A007609.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1095 from Jean-François Alcover)
• Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Crossrefs

Cf. A000203, A007609, A054973, A159886.

Programs

Maple

read("transforms3") ; a054973 := BFILETOLIST("b054973.txt") ;
for i from 1 to 1000 do if op(i,a054973) > 1 then printf("%d,", op(i,a054973)) ; fi; od: # R. J. Mathar, May 22 2009

Mathematica

b[n_] := Sum[Boole[DivisorSigma[1, k] == n], {k, 1, n}];
Select[Array[b, 1000], # > 1&] (* Jean-François Alcover, Apr 06 2020 *)

PARI

list(lim) = {my(s); for(k = 1, lim, s = invsigmaNum(k); if(s > 1, print1(s, ", ")));} \\ Amiram Eldar, Dec 25 2024, using Max Alekseyev's invphi.gp

Extensions

Edited and extended by R. J. Mathar, May 22 2009