OFFSET
1,2
LINKS
Ray Chandler, Table of n, a(n) for n = 1..92 (using b-file file from A007053)
FORMULA
a(n) = Sum_{i=1..n} pi(floor(2^(n/i))), where pi(n) = A000720(n). - Ridouane Oudra, Oct 26 2020
a(n) = A025528(2^n). - Pontus von Brömssen, Sep 27 2024
EXAMPLE
a(3)=6 because 2^3 has rank 6 in the sequence (2,3,4,5,7,8,9,...).
MATHEMATICA
T[i_, j_]:=Sum[Floor[j*Log[Prime[i]]/Log[Prime[h]]], {h, 1, PrimePi[Prime[i]^j]}]; Flatten[Table[T[i, j], {i, 1, 1}, {j, 1, 22}]]
f[n_] := Sum[ PrimePi[ Floor[2^(n/k)]], {k, n + 1}]; Array[f, 34] (* Robert G. Wilson v, Jul 08 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Clark Kimberling, Dec 13 2010
EXTENSIONS
Minor edits by Ray Chandler, Aug 20 2021
STATUS
approved