A181518 a(n) is the number for which 2^A181516(n)||(2*a(n))!

2, 4, 7, 11, 13, 16, 22, 25, 28, 35, 37, 38, 41, 47, 50, 52, 56, 59, 64, 67, 70, 76, 88, 93, 97, 98, 100, 117, 122, 133, 137, 140, 143, 148, 158, 171, 176, 179, 182, 186, 193, 196, 200, 203, 213, 218, 223, 227, 233, 234, 236, 242, 247, 248, 253, 262, 280, 290, 299

Offset

1,1

Comments

Numbers m such that Sum_{k >= 0} floor(m/2^k) is a prime. - Clark Kimberling, Feb 13 2025

Links

Table of n, a(n) for n=1..59.

Maple

isA011371 := proc(n) option remember; local k, a; for k from 0 do a := A011371(k) ; if a > n then return false; elif a = n then return true; end if; end do: end proc:
A181516 := proc(n) option remember; local a; if n = 1 then 3; else for a from procname(n-1)+1 do if isprime(a) then if isA011371(a) then return a; end if; end if; end do; end if; end proc:
A181518 := proc(n) for m from 1 do if A011371(m) = A181516(n) then return m/2 ; end if; end do: end proc: # R. J. Mathar, Nov 04 2010

Mathematica

f[n_] := Sum[Floor[n/2^k], {k, 0, Floor[Log[2, n]]}]  (* A005187 *)
Select[Range[400], PrimeQ[f[#]] &] (* Clark Kimberling, Feb 13 2025 *)

Crossrefs

Cf. A000040, A005187.

Sequence in context: A229618 A087285 A107791 * A262231 A356133 A191323

Adjacent sequences: A181515 A181516 A181517 * A181519 A181520 A181521

Keyword

nonn

Author

Vladimir Shevelev, Oct 26 2010

Extensions

Corrected (88 inserted, 129 replaced by 179) and extended beyond 227 by R. J. Mathar, Nov 04 2010

Status

approved