A073922 a(1) = 1, a(n) = smallest composite number greater than n and not occurring earlier if n is prime, or smallest prime number greater than n and not occurring earlier if n is composite.

1, 4, 6, 5, 8, 7, 9, 11, 13, 17, 12, 19, 14, 23, 29, 31, 18, 37, 20, 41, 43, 47, 24, 53, 59, 61, 67, 71, 30, 73, 32, 79, 83, 89, 97, 101, 38, 103, 107, 109, 42, 113, 44, 127, 131, 137, 48, 139, 149, 151, 157, 163, 54, 167, 173, 179, 181, 191, 60, 193, 62, 197, 199

Offset: 1

Author

Amarnath Murthy, Aug 19 2002

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A026239.

Programs

Maple

p:= 1: c:= 1: R:= 1:
for n from 2 to 100 do
  if isprime(n) then
    c:= max(c,n)+1;
    while isprime(c) do c:=c+1 od:
    R:= R,c
  else
    p:= nextprime(max(p,n));
    R:= R,p
  fi
od:
R; # Robert Israel, Apr 10 2024

Extensions

Extended by Ray Chandler, Apr 09 2014