A134928 Triple composites.

4, 6, 8, 10, 12, 14, 16, 18, 20, 28, 30, 32, 40, 42, 44, 58, 60, 62, 70, 72, 74, 100, 102, 104, 106, 108, 110, 136, 138, 140, 148, 150, 152, 178, 180, 182, 190, 192, 194, 196, 198, 200, 226, 228, 230, 238, 240, 242, 268, 270, 272, 280, 282, 284

Offset

1,1

Comments

Numbers that are composites and nearest-neighbors of twin primes.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Omar E. Pol, Determinacion geometrica de los numeros primos y compuesto.

Example

28, 30 and 32 are triple composites because 29 and 31 are twin primes and 28, 30 and 32 are composites and nearest-neighbors of 29 and 31.

Mathematica

#[[1]]+{-1, 1, 3}&/@Select[Partition[Prime[Range[3, 100]], 2, 1], #[[2]]-#[[1]]==2&]//Flatten (* Harvey P. Dale, Jun 09 2023 *)
Flatten[{#[[1]], #[[1]]+2, #[[2]]}&/@SequencePosition[Table[Which[CompositeQ[ n], 1, PrimeQ[ n], 2, True, 0], {n, 300}], {1, 2, 1, 2, 1}]] (* Harvey P. Dale, Sep 07 2023 *)

Crossrefs

Cf. Twin primes = A001097, Composite numbers = A002808.

Sequence in context: A210939 A175246 A353537 * A279040 A141109 A333197

Adjacent sequences: A134925 A134926 A134927 * A134929 A134930 A134931

Keyword

easy,nonn

Author

Omar E. Pol, Nov 16 2007

Status

approved