A168389 a(n) = PrimePi(A147819(n)).

1, 2, 3, 4, 4, 5, 6, 6, 7, 8, 8, 9, 9, 10, 11, 11, 12, 12, 13, 14, 14, 15, 15, 16, 16, 17, 18, 18, 19, 19, 20, 21, 21, 22, 22, 23, 23, 24, 24, 25, 25, 26, 27, 27, 28, 29, 29, 30, 30, 31, 31, 32, 32, 33, 34, 34, 35, 36, 36, 37, 37, 38, 38, 39, 39, 40, 40, 41, 42, 42, 43, 44, 44, 45

Offset

1,2

Links

Table of n, a(n) for n=1..74.

Maple

A147819 := proc(n) if n = 1 then 2; else for a from procname(n-1)+1 do if isprime(a-1) or isprime(a+1) then if a <> 3 then return a; end if; end if; end do ; end if; end proc: A168389 := proc(n) numtheory[pi](A147819(n)) ; end proc: seq(A168389(n), n=1..100) ; # R. J. Mathar, Dec 03 2009

Crossrefs

Cf. A000720, A147819.

Sequence in context: A196266 A340792 A112232 * A039708 A189730 A249569

Adjacent sequences: A168386 A168387 A168388 * A168390 A168391 A168392

Keyword

nonn

Author

Giovanni Teofilatto, Nov 24 2009

Extensions

Extended beyond a(26) by R. J. Mathar, Dec 03 2009

Status

approved