A227869 - OEIS

%I #18 Oct 09 2023 17:04:17

%S 187,217,247,427,517,637,667,697,817,847,1027,1057,1147,1177,1207,

%T 1267,1357,1387,1417,1477,1507,1537,1687,1717,1807,1837,1897,1927,

%U 1957,2047,2077,2107,2167,2197,2227,2257,2317,2407,2497,2527,2587,2737,2827,2947,2977

%N Composite numbers congruent to 7 (mod 30).

%C Up to 4897, there are more primes than composites among the numbers of the form 7+30k, only from 4927 on, composite numbers become more frequent.

%C See A132231 for primes of that form. See also A132237 (primes = 7 or 23 (mod 30)) and A229947 (primes not = 7 or 23 (mod 30)).

%H Harvey P. Dale, <a href="/A227869/b227869.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Table[30n + 7, {n, 100}], Not[PrimeQ[#]] &] (* _Alonso del Arte_, Nov 03 2013 *)

%t Select[Range[7,3000,30],CompositeQ] (* _Harvey P. Dale_, Oct 09 2023 *)

%o (PARI) forstep(p=7,1999,30,isprime(p)||print1(p","))

%K nonn

%O 1,1

%A _M. F. Hasler_, Nov 02 2013