A282028 -id:A282028 - cp's OEIS frontend

A143545 a(n) = n unless n is a prime, in which case a(n) = 2n.

1, 4, 6, 4, 10, 6, 14, 8, 9, 10, 22, 12, 26, 14, 15, 16, 34, 18, 38, 20, 21, 22, 46, 24, 25, 26, 27, 28, 58, 30, 62, 32, 33, 34, 35, 36, 74, 38, 39, 40, 82, 42, 86, 44, 45, 46, 94, 48, 49, 50, 51, 52, 106, 54, 55, 56, 57, 58, 118, 60, 122, 62, 63, 64, 65, 66, 134, 68, 69, 70, 142

Offset: 1

Gary W. Adamson, Aug 23 2008

nonn

			a(3) = 6 = 2*3 since 3 is prime.
a(4) = 4 since 4 is a nonprime.

N. J. A. Sloane, Table of n, a(n) for n = 1..10000

Cf. A066560, A143544, A061397.

See A282028 for another version.

a(n) = n + A061397(n), where A061397 = (0, 2, 3, 0, 5, 0, 7,...).
Equals row sums of triangle A143544.
a(n)=A066560(n), n>1. [From R. J. Mathar, Sep 05 2008]

Extended beyond a(14) by R. J. Mathar, Sep 05 2008

A282029 a(n) = n - pi(n/2).

Original entry on oeis.org

0, 1, 2, 3, 3, 4, 4, 5, 6, 7, 7, 8, 9, 10, 10, 11, 12, 13, 14, 15, 16, 17, 17, 18, 19, 20, 20, 21, 22, 23, 24, 25, 26, 27, 27, 28, 29, 30, 30, 31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 48, 49, 50, 51, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 62, 63, 64, 65, 66, 67, 68

Offset: 0

N. J. A. Sloane, Feb 17 2017

nonn

Vincenzo Librandi, Table of n, a(n) for n = 0..10000

Cf. A000720, A282028.

[0,1] cat [ n-#PrimesUpTo(n div 2): n in [2..90] ]; // Vincenzo Librandi, Feb 18 2017

Table[n - PrimePi[n/2], {n, 0, 100}] (* Vincenzo Librandi, Feb 18 2017 *)

a(n)=n - primepi(n\2) \\ Charles R Greathouse IV, Feb 18 2017

cp's OEIS Frontend

A143545 a(n) = n unless n is a prime, in which case a(n) = 2n.

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A282029 a(n) = n - pi(n/2).

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