OFFSET
1,1
COMMENTS
Numbers k such that the number of groups of order k (when greater than 1) divides the group order k. I require a proper divisor > 1 because trivially for any p there is 1 group (the cyclic group) of order p, and 1 | p. Even semiprimes A100484 are a proper subset, because when k = p*q for primes p and q, then A000001(k) = 1 if gcd(p,q-1) = 1, 2 if gcd(p,q-1) = p, and (p < q).
LINKS
Nathaniel Johnston, Table of n, a(n) for n = 1..324
EXAMPLE
a(11) = 42 is in the sequence because there are 6 nonisomorphic groups of order 42, and 42/6 = 7.
a(18) = 75 is the first odd value, because there are 5 nonisomorphic groups of order 75, and 75/5 = 15. The next odd value is 125.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Feb 13 2011
EXTENSIONS
a(44) - a(52) from Nathaniel Johnston, Apr 26 2011
STATUS
approved