A216816 - OEIS

A216816

Primes congruent to 3 or 7 mod 20.

3, 7, 23, 43, 47, 67, 83, 103, 107, 127, 163, 167, 223, 227, 263, 283, 307, 347, 367, 383, 443, 463, 467, 487, 503, 523, 547, 563, 587, 607, 643, 647, 683, 727, 743, 787, 823, 827, 863, 883, 887, 907, 947, 967, 983, 1063, 1087, 1103, 1123, 1163, 1187, 1223, 1283, 1303, 1307, 1327, 1367, 1423, 1427, 1447, 1483, 1487

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OFFSET

1,1

COMMENTS

This is a subsequence of A106865 but it is an important sequence in its own right.

This may actually be the same sequence as A122870, I did not check. If it is, I will merge the two entries.

(a(n) = A122870(n) at least up to n <= 8800. - R. J. Mathar, Sep 25 2012)

REFERENCES

David A. Cox, "Primes of the Form x^2 + n y^2", Wiley, 1989; see p. 33.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

MATHEMATICA

Select[Prime[Range[300]], MemberQ[{3, 7}, Mod[#, 20]]&] (* Vincenzo Librandi, Jan 06 2013 *)

PROG

(Magma) [p: p in PrimesUpTo(1500) | p mod 20 in [3, 7]]; // Vincenzo Librandi, Jan 06 2013

CROSSREFS

A subsequence of A106865. Cf. A216815, A122870.

Sequence in context: A084739 A133434 A122870 * A079477 A014426 A054270

Adjacent sequences: A216813 A216814 A216815 * A216817 A216818 A216819

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Sep 20 2012

STATUS

approved