OFFSET
1,1
COMMENTS
a(p) = p^2 + p +1, a(2^m) = 3*2^m +1,a(p^m) = p^m + p^(m+1) +1, if p is a prime.
EXAMPLE
a(5) = 31 as there are 5 non-coprime numbers to 5 between 5 and 31, i.e. 10,15,20,25 and 30.
PROG
(PARI) print1("3, "):for(n=2, 100, s=0:for(k=n+1, 10^9, if(gcd(n, k)>1, s=s+1): if(s==n, s=k:break)):print1(s+1", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Oct 30 2002
EXTENSIONS
More terms from Ralf Stephan, Mar 25 2003
STATUS
approved