OFFSET
1,2
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..3000
EXAMPLE
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}.
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
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 05 2001
EXTENSIONS
a(9) - a(45) from Nathaniel Johnston, Apr 29 2011
STATUS
approved