A216815 Primes congruent to 1 or 9 mod 20.

29, 41, 61, 89, 101, 109, 149, 181, 229, 241, 269, 281, 349, 389, 401, 409, 421, 449, 461, 509, 521, 541, 569, 601, 641, 661, 701, 709, 761, 769, 809, 821, 829, 881, 929, 941, 1009, 1021, 1049, 1061, 1069, 1109, 1129, 1181, 1201, 1229, 1249, 1289, 1301, 1321, 1361, 1381, 1409, 1429, 1481, 1489, 1549, 1601, 1609, 1621, 1669, 1709, 1721, 1741, 1789, 1801, 1861

Offset

1,1

Comments

This is a subsequence of A033205 but it is an important sequence in its own right.

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[{1, 9}, Mod[#, 20]]&] (* Vincenzo Librandi, Mar 22 2013 *)

Prog

(Magma) [p: p in PrimesUpTo(2000) | p mod 20 in [1, 9]]; // Vincenzo Librandi, Mar 22 2013

Crossrefs

A subsequence of A033205. Cf. A216816.

Sequence in context: A343478 A343479 A080899 * A157141 A107218 A346145

Adjacent sequences: A216812 A216813 A216814 * A216816 A216817 A216818

Keyword

nonn,easy

Author

N. J. A. Sloane, Sep 20 2012

Status

approved