A159953 - OEIS

%I #20 Dec 26 2024 03:55:45

%S 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,

%T 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,

%U 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

%N Values in A054973 larger than 1.

%C 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.

%H Amiram Eldar, <a href="/A159953/b159953.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1095 from Jean-François Alcover)

%H Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).

%p read("transforms3") ; a054973 := BFILETOLIST("b054973.txt") ;

%p 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

%t b[n_] := Sum[Boole[DivisorSigma[1, k] == n], {k, 1, n}];

%t Select[Array[b, 1000], # > 1&] (* _Jean-François Alcover_, Apr 06 2020 *)

%o (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

%Y Cf. A000203, A007609, A054973, A159886.

%K nonn

%O 1,1

%A _Jaroslav Krizek_, Apr 27 2009

%E Edited and extended by _R. J. Mathar_, May 22 2009