This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A141881 #20 Nov 23 2024 13:10:09 %S A141881 41,61,101,181,241,281,401,421,461,521,541,601,641,661,701,761,821, %T A141881 881,941,1021,1061,1181,1201,1301,1321,1361,1381,1481,1601,1621,1721, %U A141881 1741,1801,1861,1901,2081,2141,2161,2221,2281,2341,2381,2441,2521,2621,2741,2801 %N A141881 Primes congruent to 1 mod 20. %C A141881 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 %H A141881 Vincenzo Librandi, <a href="/A141881/b141881.txt">Table of n, a(n) for n = 1..1000</a> %H A141881 David Brink, <a href="http://www.sciencedirect.com/science/article/pii/S0022314X08001145">Five peculiar theorems on simultaneous representation of primes by quadratic forms</a>, Journal of Number Theory 129(2) (2009), 464-468, doi:10.1016/j.jnt.2008.04.007, MR 2473893 %p A141881 select(isprime,[seq(20*i+1,i=1..1000)]); # _Robert Israel_, Jun 11 2014 %t A141881 Select[Range[1,5000,20],PrimeQ[#]&] (* _Vladimir Joseph Stephan Orlovsky_, Mar 31 2011*) %t A141881 Select[Prime[Range[500]],Mod[#,20]==1&] (* _Harvey P. Dale_, Nov 23 2024 *) %o A141881 (Magma) [p: p in PrimesUpTo(3000) | p mod 20 eq 1 ]; // _Vincenzo Librandi_, Aug 15 2012 %o A141881 (PARI) is(n)=isprime(n) && n%20==1 \\ _Charles R Greathouse IV_, Jul 01 2016 %Y A141881 Cf. A000040, A105854, A141882, A141883. %K A141881 nonn,easy %O A141881 1,1 %A A141881 _N. J. A. Sloane_, Jul 11 2008