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A216816 Primes congruent to 3 or 7 mod 20. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is a subset 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 subset 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

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Last modified September 19 04:52 EDT 2019. Contains 327187 sequences. (Running on oeis4.)