OFFSET
3,1
COMMENTS
For n = 1, a(1) = 1; for n = 2 there is no solution.
For n in A002982, a(n) = n!-1.
REFERENCES
R. K. Guy (1981): Unsolved Problems In Number Theory, B39.
LINKS
Ray Chandler, Table of n, a(n) for n=3..52
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.
FORMULA
EXAMPLE
For n = 6, the 15 solutions are as follows: {264, 270, 280, 354, 376, 406, 418, 435, 459, 478, 537, 623, 649, 667, 719}.
PROG
(PARI) a(n) = {fn = n!; x = fn - 1; while(sigma(x) != fn, x--); x; } \\ Michel Marcus, Dec 17 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jun 28 2000
EXTENSIONS
More terms from Jud McCranie, Oct 09 2000
a(15) from Donovan Johnson, Aug 31 2008
a(16)-a(19) from Donovan Johnson, Nov 22 2008
a(20)-a(52) from Ray Chandler, Jan 15 2009
STATUS
approved