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 A380549 #18 Mar 21 2025 02:23:56
%S A380549 8,13,15,18,22,23,24,28,29,33,35,36,38,42,43,46,48,50,51,53,57,58,60,
%T A380549 61,63,64,68,69,71,73,74,78,79,80,83,85,87,88,90,92,93,96,97,98,99,
%U A380549 100,101,103,105,106,108,112,113,114,118,120,123,126,127,128,131,132,133,134,137,138,139,141,143,145,148,150
%N A380549 List of numbers of the form i + 3*j + 4*i*j for i, j >= 1.
%C A380549 This is a companion sequence to A380509. If N != 6 is a positive integer not in this list then 4*N + 3 is either a prime or three times a prime. See A380550.
%C A380549 Compare with A072668, numbers of the form i + j + i*j, and A047845, numbers of the form i + j + 2*i*j.
%p A380549 L := 150: S := {}:
%p A380549 for i from 1 to L do
%p A380549 for j from 1 to L do
%p A380549 if i + 3*j + 4*i*j <= L then S := `union`(S, {i+3*j+4*i*j}) end if
%p A380549 end do;
%p A380549 end do:
%p A380549 S;
%Y A380549 Cf. A047845, A072668, A380509, A380550.
%K A380549 nonn,easy
%O A380549 1,1
%A A380549 _Peter Bala_, Jan 26 2025