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A073432 Numbers n such that prime(n) + composite(n) is even. 3
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 (list; graph; refs; listen; history; text; internal format)
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: A009023 A099309 A235865 * A133803 A188069 A190697

Adjacent sequences:  A073429 A073430 A073431 * A073433 A073434 A073435

KEYWORD

nonn,easy

AUTHOR

Labos Elemer, Jul 31 2002

STATUS

approved

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Last modified March 28 22:27 EDT 2017. Contains 284249 sequences.