OFFSET
0,5
COMMENTS
A110078(n) gives number of solutions of the equation sigma(x)=10^n.
Conjecture: For n>3 a(n) is positive.
LINKS
Max Alekseyev, Table of n, a(n) for n = 0..1000
Max Alekseyev, PARI/GP scripts for miscellaneous math problems
Max A. Alekseyev, Computing the Inverses, their Power Sums, and Extrema for Euler's Totient and Other Multiplicative Functions. Journal of Integer Sequences, Vol. 19 (2016), Article 16.5.2
EXAMPLE
a(9)=590624811 because sigma(590624811)=sigma(3^3*7*3124999) sigma(3^3)*sigma(7)*sigma(3124999)=40*8*3125000=10^9 and 590624811 is the smallest number m with this property (sigma(m)=10^9).
PROG
(PARI) { a(n) = invsigma(10^n)[1] } \\ Max Alekseyev, Apr 26 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, Aug 01 2005
EXTENSIONS
a(10)-a(11) from Donovan Johnson and Farideh Firoozbakht, Nov 22 2008
a(12) onward from Max Alekseyev, Apr 26 2010, Mar 06 2014
STATUS
approved