OFFSET
1,1
COMMENTS
m<a(n): #{k: k>spf(k)^n & 1<=k<=m} <= m/2;
m>=a(n): #{k: k>spf(k)^n & 1<=k<=m} > m/2.
FORMULA
Numbers so far satisfy a(n) = 3^n + 3*2^n + 6. - Ralf Stephan, May 10 2004
Empirical G.f.: 3*x*(5-21*x+20*x^2)/(1-x)/(1-2*x)/(1-3*x). - Colin Barker, Feb 22 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 29 2003
EXTENSIONS
a(14)-a(24) from Giovanni Resta, May 23 2013
STATUS
approved