A073432 Numbers n such that prime(n) + composite(n) is even.

1, 4, 8, 12, 15, 17, 21, 23, 26, 30, 33, 35, 38, 40, 44, 46, 49, 53, 55, 58, 61, 63, 66, 68, 70, 73, 77, 81, 84, 86, 88, 90, 92, 94, 97, 100, 102, 106, 108, 110, 112, 116, 118, 121, 123, 126, 129, 131, 134, 136, 140, 142, 144, 146, 150, 154, 156, 158, 160, 162, 165

Offset

1,2

Comments

For n > 1, numbers n such that the n-th composite number is odd. - Charles R Greathouse IV, Apr 03 2012

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

Numbers n such that (A000040(n)+A002808(n))/2 is an integer.

a(n) ~ 2n since the primes have density 0. Charles R Greathouse IV, Apr 03 2012

Example

8 is in the sequence since prime(8)=19, composite(8)=15, and their average 17 is an integer.

Mathematica

c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x] Do[s=(Prime[n]+c[n])/2; If[IntegerQ[s], Print[s]], {n, 1, 256}]

Prog

(PARI) print1(n=1); for(c=6, 1e3, if(isprime(c), next); n++; if(c%2, print1(", "n))) \\ Charles R Greathouse IV, Apr 03 2012

Crossrefs

Cf. A000040, A002808.

Sequence in context: A311087 A311088 A311089 * A311090 A311091 A133803

Adjacent sequences: A073429 A073430 A073431 * A073433 A073434 A073435

Keyword

nonn,easy

Author

Labos Elemer, Jul 31 2002

Status

approved