A227868 Composite numbers congruent to 7 or 23 (mod 30).

143, 187, 203, 217, 247, 323, 413, 427, 473, 517, 533, 623, 637, 667, 697, 713, 803, 817, 833, 847, 893, 923, 1027, 1043, 1057, 1073, 1133, 1147, 1177, 1207, 1253, 1267, 1313, 1343, 1357, 1387, 1403, 1417, 1463, 1477, 1507, 1537, 1643

Offset: 1

Author

M. F. Hasler, Nov 02 2013

Keywords

• nonn

Comments

It is remarkable that up to 4913, numbers congruent to 7 or 23 (mod 30) are more frequently prime than composite.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..2000

Crossrefs

Cf. A132237, A229947.

Programs

Mathematica

Select[Range[2000],CompositeQ[#]&&MemberQ[{7,23},Mod[#,30]]&] (* Harvey P. Dale, Sep 21 2024 *)

PARI

for(p=1,1999,setsearch([7,23],p%30)&&!isprime(p)&&print1(p","))