A099049 Numbers n such that n-1 and n+1 are both prime or both composite.

4, 5, 6, 7, 9, 11, 12, 13, 15, 17, 18, 19, 21, 23, 25, 26, 27, 29, 30, 31, 33, 34, 35, 37, 39, 41, 42, 43, 45, 47, 49, 50, 51, 53, 55, 56, 57, 59, 60, 61, 63, 64, 65, 67, 69, 71, 72, 73, 75, 76, 77, 79, 81, 83, 85, 86, 87, 89, 91, 92, 93, 94, 95, 97, 99, 101, 102, 103, 105, 107

Offset

1,1

Links

Table of n, a(n) for n=1..70.

Mathematica

Select[Range[120], AllTrue[#+{1, -1}, CompositeQ]||AllTrue[#+{1, -1}, PrimeQ]&] (* Harvey P. Dale, Sep 01 2021 *)

Prog

(PARI) for(n=3, 200, s=isprime(n-1)+isprime(n+1); if(s<>1, print1(n, ", ")))

Crossrefs

Sequence in context: A075862 A088685 A022299 * A217128 A036668 A260997

Adjacent sequences: A099046 A099047 A099048 * A099050 A099051 A099052

Keyword

nonn

Author

Rick L. Shepherd, Nov 13 2004

Status

approved