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 A216815 Primes congruent to 1 or 9 mod 20. 5
 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 subset 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 subset of A033205. Cf. A216816. Sequence in context: A069454 A035789 A080899 * A157141 A107218 A058900 Adjacent sequences:  A216812 A216813 A216814 * A216816 A216817 A216818 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Sep 20 2012 STATUS approved

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Last modified July 22 16:24 EDT 2019. Contains 325224 sequences. (Running on oeis4.)