A063975 Smallest numbers such that the number of terms in inverse set usigma equals n; where usigma = A034448.

1, 12, 24, 60, 120, 72, 216, 288, 1320, 480, 240, 840, 1296, 2700, 960, 1512, 1080, 720, 1728, 2016, 3840, 3240, 3456, 2520, 3360, 3024, 1440, 3600, 6912, 2160, 19152, 2880, 7920, 13680, 9072, 12600, 6048, 5040, 18000, 6480, 27216, 13440, 7200, 27648, 5760

Offset: 1

Author

Labos Elemer, Sep 05 2001

Keywords

• nonn

Examples

			usigma(x) = 288, invusigma(288) = {138, 154, 165, 168, 213, 235, 248, 253}, so a(288) = 8, the number of all terms in the inverse set and all similar numbers are larger: {288, 648, 672, 900}.
		

Links

• Donovan Johnson, Table of n, a(n) for n = 1..3000

Crossrefs

Cf. A034444, A034448, A051444, A054973, A057637.

Programs

Maple

with(numtheory): A034448 := proc(n) option remember: local ans,i: ans:=1: for i from 1 to nops(ifactors(n)[2]) do ans := ans*(1+ifactors(n)[ 2 ][ i ][ 1 ]^ifactors(n)[ 2 ] [ i ] [ 2 ]): od: return ans: end: for n from 1 to 5000 do m:=A034448(n): if(type(ct[m],integer))then ct[m]:=ct[m]+1: else ct[m]:=1: fi:od: for m from 1 to 28 do for n from 1 to 5000 do if(ct[n]=m)then printf("%d, ",n):break: fi: od:od: # Nathaniel Johnston, Apr 29 2011

Extensions

a(9) - a(45) from Nathaniel Johnston, Apr 29 2011