A100319 -id:A100319 - cp's OEIS frontend

A100318 Numbers n such that at least one of n-1 and n+1 is composite.

3, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 80, 81

Offset: 1

Rick L. Shepherd, Nov 13 2004

nonn

All odd numbers > 1 occur in this sequence. For the subsequence of even terms, see A100319.

G. C. Greubel, Table of n, a(n) for n = 1..10000

Cf. A100317 (exactly one of n-1 and n+1 is prime/composite), A100319.

[n: n in [3..100] | not IsPrime(n-1) or not IsPrime(n+1) ]; // G. C. Greubel, Apr 25 2019

Select[Range[3, 100], CompositeQ[#-1] || CompositeQ[#+1] &] (* G. C. Greubel, Apr 25 2019 *)

for(n=3,100,if(isprime(n-1)+isprime(n+1)<=1,print1(n,",")))

[n for n in (3..100) if (is_prime(n-1) + is_prime(n+1) <= 1)] # G. C. Greubel, Apr 24 2019

A167692 The even nonisolated nonprimes.

Original entry on oeis.org

0, 8, 10, 14, 16, 20, 22, 24, 26, 28, 32, 34, 36, 38, 40, 44, 46, 48, 50, 52, 54, 56, 58, 62, 64, 66, 68, 70, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 104, 106, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 140, 142, 144, 146, 148

Offset: 1

Juri-Stepan Gerasimov, Nov 09 2009

Zero together with A100319, the even numbers n such that at least one of n-1 and n+1 is composite.

G. C. Greubel, Table of n, a(n) for n = 1..1000

Cf. A100319, A164276.

Select[Range[0, 100], Mod[#, 2] == 0 && !PrimeQ[#] && (! PrimeQ[# - 1] || !PrimeQ[# + 1]) &] (* G. C. Greubel, Jul 07 2016 *)
Join[{0},Select[Range[2,150,2],AnyTrue[#+{1,-1},CompositeQ]&]] (* Harvey P. Dale, Nov 10 2024 *)

isA167692(n) = (n%2==0)&&!isprime(n)&&(!isprime(n-1)||!isprime(n+1)) \\ Michael B. Porter, Feb 02 2010

Edited by Charles R Greathouse IV, Mar 22 2010

cp's OEIS Frontend

A100318 Numbers n such that at least one of n-1 and n+1 is composite.

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