A181962 - OEIS

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A181962

Numbers not expressed in form pi(n)+pi(sqrt(n)) with prime n.

3, 6, 12, 19, 35, 45, 68, 80, 108, 156, 173, 231, 276, 297, 344, 425, 504, 537, 628, 695, 726, 833, 909, 1024, 1188, 1278, 1321, 1409, 1452, 1553, 1908, 2008, 2174, 2224, 2524, 2583, 2766, 2953, 3082, 3281, 3477, 3554, 3911, 3989, 4134, 4210, 4674, 5154, 5323

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OFFSET

1,1

COMMENTS

Or places of squares in A000430.

LINKS

Table of n, a(n) for n=1..49.

EXAMPLE

12 is in the sequence, since pi(23)+pi(sqrt(23))=9+2=11, while pi(29)+pi(sqrt(29))=10+3=13.

Also 12 is in the sequence since A000430(12)=25 is not prime.

MATHEMATICA

t = Table[PrimePi[n] + PrimePi[Sqrt[n]], {n, Prime[Range[10000]]}]; Complement[Range[t[[-1]]], t] (* T. D. Noe, Apr 09 2012 *)