OFFSET
1,1
COMMENTS
For known terms the number of solutions is prime.
All known terms are nonsquarefree.
The terms of this sequence that have a nonprime number of solutions are 195200, 248000, 941600, 980784, ... . There are no squarefree terms below 10^8. - Amiram Eldar, Nov 16 2024
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
FORMULA
EXAMPLE
20 is a term because 25 is the least solution of 20 = A000010(x) and the number of solutions 5, divides 20 and 25.
204 is a term because 309 is the least solution of 204 = A000010(x) and the number of solutions 3, divides 204 and 309.
1764 is a term because 2107 is the least solution of 1764 = A000010(x) and the number of solutions 7, divides 1764 and 2107.
10 is not a term because 11 is the least solution of 10 = A000010(x) and the number of solutions 2, does not divide 10 and 11.
PROG
(PARI) is(k) = {my(ns = invphiNum(k)); ns > 0 && !(k % ns) && !(invphiMin(k) % ns); } \\ Amiram Eldar, Nov 16 2024, using Max Alekseyev's invphi.gp
CROSSREFS
KEYWORD
nonn
AUTHOR
Torlach Rush, Apr 13 2018
STATUS
approved