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 A380572 #13 Jan 31 2025 04:23:12
%S A380572 1,2,3,4,5,7,8,9,10,13,14,15,17,18,22,23,24,25,27,28,32,34,35,37,39,
%T A380572 43,44,45,48,49,50,53,57,58,59,60,62,64,67,69,70,73,77,78,79,80,84,87,
%U A380572 88,93,95,97,98,99,100,102,104,105,108,111,112,113,114,115,122
%N A380572 Complement of A380509.
%C A380572 4*a(n) + 1 or (4*a(n) + 1)/3 is a prime number.
%C A380572 Compare with A380550, numbers not of the form i + 3*j + 4*i*j. See also A006093, numbers not of the form i + j + i*j and A005097, numbers not of the form i + j + 2*i*j. - _Peter Bala_, Jan 30 2025
%H A380572 Peter Bala, <a href="/A380572/a380572_1.pdf">4*A380572(n) + 1 is either a prime or three times a prime</a>
%p A380572 S := {}:
%p A380572 for n from 1 to 150 do
%p A380572 if isprime(4*n+1) then S := `union`(S, {n}) fi;
%p A380572 if type((4*n+1)*(1/3), integer) then if isprime((4*n+1)*(1/3)) then S := `union`(S, {n}) fi; fi;
%p A380572 end do:
%p A380572 S; # _Peter Bala_, Jan 30 2025
%Y A380572 Cf. A005097, A006093, A380509, A380550.
%K A380572 nonn
%O A380572 1,2
%A A380572 _Davide Rotondo_, Jan 27 2025