OFFSET
1,1
COMMENTS
REFERENCES
J. Touchard, "Propriétés arithmétiques de certains nombres récurrents", Ann. Soc. Sci. Bruxelles A 53 (1933), pp. 21-31.
LINKS
Eric Weisstein's World of Mathematics, Touchard's Congruence
EXAMPLE
For n=3, a(3)=11, Bell(11)=678570, Bell(11) - 2 = 11^2 * 61688.
MATHEMATICA
Select[Prime[Range[1000]], Divisible[BellB[#]-2, #^2] &]
CROSSREFS
KEYWORD
nonn,hard,more,nice
AUTHOR
Amiram Eldar, Mar 04 2017
EXTENSIONS
a(7) from Hiroaki Yamanouchi, Aug 30 2018
STATUS
approved