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A141881
Primes congruent to 1 mod 20.
19
41, 61, 101, 181, 241, 281, 401, 421, 461, 521, 541, 601, 641, 661, 701, 761, 821, 881, 941, 1021, 1061, 1181, 1201, 1301, 1321, 1361, 1381, 1481, 1601, 1621, 1721, 1741, 1801, 1861, 1901, 2081, 2141, 2161, 2221, 2281, 2341, 2381, 2441, 2521, 2621, 2741, 2801
OFFSET
1,1
COMMENTS
Such a prime is representable by either both or neither of the quadratic forms x^2 + 20 y^2 and x^2 + 100 y^2. See the Brink link. - Robert Israel, Jun 11 2014
LINKS
David Brink, Five peculiar theorems on simultaneous representation of primes by quadratic forms, Journal of Number Theory 129(2) (2009), 464-468, doi:10.1016/j.jnt.2008.04.007, MR 2473893
MAPLE
select(isprime, [seq(20*i+1, i=1..1000)]); # Robert Israel, Jun 11 2014
MATHEMATICA
Select[Range[1, 5000, 20], PrimeQ[#]&] (* Vladimir Joseph Stephan Orlovsky, Mar 31 2011*)
PROG
(Magma) [p: p in PrimesUpTo(3000) | p mod 20 eq 1 ]; // Vincenzo Librandi, Aug 15 2012
(PARI) is(n)=isprime(n) && n%20==1 \\ Charles R Greathouse IV, Jul 01 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jul 11 2008
STATUS
approved