A227868 - OEIS

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

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OFFSET

1,1

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

MATHEMATICA

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

PROG

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

CROSSREFS

Cf. A132237, A229947.

Sequence in context: A097435 A350735 A073954 * A353059 A176876 A257767

Adjacent sequences: A227865 A227866 A227867 * A227869 A227870 A227871

KEYWORD

nonn

AUTHOR

M. F. Hasler, Nov 02 2013

STATUS

approved