A121543 "If k appears then the k-th prime doesn't", with a(1)=1.

1, 3, 4, 6, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 41, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 67, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 83, 84, 85, 86, 87, 88

Offset: 1

Author

Zak Seidov, Aug 06 2006

Keywords

• nonn

Comments

Most prime numbers are absent; from first 1000 primes only 138 are terms: 3, 11, 17, 41, 67, 83, 109, 127, 157, 191, 211, 241, 277, 283, 353, ..., all with prime indices. Also, all nonprimes are terms. - Zak Seidov, Sep 12 2015

k is a term if and only if A078442(k) is even. - Pontus von Brömssen, Jul 25 2025

Links

• Zak Seidov, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A078442, A262275.

Programs

Mathematica

s={1};Do[If[ !PrimeQ[n]||(PrimeQ[n] && FreeQ[s,PrimePi[n]]),AppendTo[s,n]],{n,2,100}];s (* Zak Seidov *)