OFFSET
2,1
COMMENTS
a(n) is the index of the first occurrence of n in A107609.
Lim_{n->infinity} a(n+1)/a(n) ~ e.
FORMULA
a(n) = min { k >= 2 : round(k/pi(k)) = n }.
EXAMPLE
a(2) = 16 because round(16/pi(16)) = round(16/6) = 3 and for no number less than 16 does the quotient equal 3.
MATHEMATICA
f[n_] := Round[ n / PrimePi[ n]]; g[2] = 2; g[n_] := g[n] = Block[{k = PrimePi[E g[n - 1]]}, While[ f[k] < n, k++ ]; k]; Do[ Print[ g[ n]], {n, 2, 26}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post and Robert G. Wilson v, May 17 2005
STATUS
approved