A159559 -id:A159559 - cp's OEIS frontend

A163578 If n is prime, a(n) is next composite greater than a(n-1), else if n is composite, a(n) is next prime greater than a(n-1) else 2.

2, 4, 6, 7, 8, 11, 12, 13, 17, 19, 20, 23, 24, 29, 31, 37, 38, 41, 42, 43, 47, 53, 54, 59, 61, 67, 71, 73, 74, 79, 80, 83, 89, 97, 101, 103, 104, 107, 109, 113, 114, 127, 128, 131, 137, 139, 140, 149, 151, 157, 163, 167, 168, 173, 179, 181, 191, 193, 194, 197, 198, 199

Offset: 1

Gerald Hillier, Jul 31 2009

			1 is not prime, a(1)=2.
2 is prime, a(2)=4.
3 is prime, a(3)=6.
4 is composite, a(4)=7.

Paolo Xausa, Table of n, a(n) for n = 1..10000

Cf. A159559, A178663.

Join[{2, 4}, FoldList[If[PrimeQ[#2], #+1, NextPrime[#]] &, 6, Range[4, 100]]] (* Paolo Xausa, Sep 03 2025 *)

More terms from Paolo Xausa, Sep 03 2025

A151994 For k=A079523(n),n>=2, let {S_k} be the minimal recursive sequence beginning with k similar to N with respect to property of integer to be or not to be in A079523. Then a(n) is the point of confluence of {S_k} with {S_5}.

Original entry on oeis.org

5, 13, 13, 29, 29, 61, 61, 61, 61

Offset: 2

Vladimir Shevelev, Jul 12 2009

nonn

			Note that, {S_5} is {5,6,8,10,13,...}(see A162736) and {S_7} is {7,8,10,11,13,...}, then a(3)=13.

Cf. A162736 A079523 A159615 A159619 A159559 A159560 A004760 A035263.

cp's OEIS Frontend

A163578 If n is prime, a(n) is next composite greater than a(n-1), else if n is composite, a(n) is next prime greater than a(n-1) else 2.

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