A380549 - OEIS

%I #18 Mar 21 2025 02:23:56

%S 8,13,15,18,22,23,24,28,29,33,35,36,38,42,43,46,48,50,51,53,57,58,60,

%T 61,63,64,68,69,71,73,74,78,79,80,83,85,87,88,90,92,93,96,97,98,99,

%U 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 List of numbers of the form i + 3*j + 4*i*j for i, j >= 1.

%C 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 Compare with A072668, numbers of the form i + j + i*j, and A047845, numbers of the form i + j + 2*i*j.

%p L := 150:  S := {}:

%p for i from 1 to L do

%p   for j from 1 to L do

%p     if i + 3*j + 4*i*j <= L then S := `union`(S, {i+3*j+4*i*j}) end if

%p   end do;

%p end do:

%p S;

%Y Cf. A047845, A072668, A380509, A380550.

%K nonn,easy

%O 1,1

%A _Peter Bala_, Jan 26 2025