A216815 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

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