A100318 - OEIS

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

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OFFSET

1,1

COMMENTS

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

LINKS

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

MATHEMATICA

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

PROG

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

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

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

CROSSREFS

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

Sequence in context: A008520 A217129 A336340 * A167707 A131903 A141114

Adjacent sequences: A100315 A100316 A100317 * A100319 A100320 A100321

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Nov 13 2004

STATUS

approved