A089268 Odd semiprimes m such that m-2 is composite.

35, 51, 57, 65, 77, 87, 93, 95, 119, 121, 123, 143, 145, 155, 161, 177, 185, 187, 203, 205, 209, 215, 217, 219, 221, 237, 247, 249, 267, 287, 289, 291, 299, 301, 303, 305, 321, 323, 327, 329, 335, 341, 365, 371, 377, 393, 395, 407, 413, 415, 417, 427, 437

Offset: 1

Author

Reinhard Zumkeller, Oct 28 2003

Keywords

• nonn

Comments

A087942(a(n)) = 0.

Assuming Goldbach's conjecture that every even number greater than 2 is the sum of two primes, these are the numbers that are the product of two primes but not the sum of two primes. - Michael B. Porter, Feb 08 2013

Links

• Bill McEachen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A062721, A046315, A001358.

Programs

Mathematica

Take[Select[Union[Flatten[Table[Prime[i] Prime[j], {i, 2, 25}, {j, 2, 25}]]], Not[PrimeQ[# - 2]] &], 50] (* Alonso del Arte, Feb 08 2013 *)

PARI

isok(m) = (m%2) && (bigomega(m)==2) && !isprime(m-2); \\ Michel Marcus, Oct 19 2021