A129131 Alternately write composite and prime numbers.

4, 2, 6, 3, 8, 5, 9, 7, 10, 11, 12, 13, 14, 17, 15, 19, 16, 23, 18, 29, 20, 31, 21, 37, 22, 41, 24, 43, 25, 47, 26, 53, 27, 59, 28, 61, 30, 67, 32, 71, 33, 73, 34, 79, 35, 83, 36, 89, 38, 97, 39, 101, 40, 103, 42, 107, 44, 109, 45, 113, 46, 127, 48, 131, 49, 137, 50, 139, 51

Offset

1,1

Comments

a(2n-1) = A073846(2n+1), a(2n) = A073846(2n).

Links

Table of n, a(n) for n=1..69.

Formula

a(n) = A066249(n) + 1. - Filip Zaludek, Dec 10 2016

Example

Lowest composite number is 4, lowest prime number is 2, next composite number after 4 is 6, next prime number after 2 is 3 and so on.

Mathematica

f[n_]:=Module[{prs=Prime[Range[n]], comps}, comps=Rest[Complement[Range[n+ Length[prs]+1], prs]]; Riffle[comps, prs]] (* Harvey P. Dale, May 10 2011 *)

Prog

(Magma) P:=[ n : n in [2..150] | IsPrime(n) ]; C:=[ n : n in [2..70] | not IsPrime(n) ]; &cat[ [C[k], P[k] ]: k in [1..Minimum(#C, #P)] ]; // Klaus Brockhaus, Mar 31 2007

Crossrefs

Cf. A000040 (prime numbers), A002808 (composite numbers), A073846 (alternate nonprime and prime numbers).

Sequence in context: A297307 A163238 A097362 * A237056 A285296 A257885

Adjacent sequences: A129128 A129129 A129130 * A129132 A129133 A129134

Keyword

nonn,easy

Author

Edwin F. Sampang, Mar 30 2007

Extensions

Edited and extended by Klaus Brockhaus, Mar 31 2007

Status

approved