A380509 Numbers of the form i+j+4ij for i,j >= 1 together with numbers of the form -i-j+4ij for i,j >= 2.

6, 11, 12, 16, 19, 20, 21, 26, 29, 30, 31, 33, 36, 38, 40, 41, 42, 46, 47, 51, 52, 54, 55, 56, 61, 63, 65, 66, 68, 71, 72, 74, 75, 76, 81, 82, 83, 85, 86, 89, 90, 91, 92, 94, 96, 101, 103, 106, 107, 109, 110, 111, 116, 117, 118, 119, 120, 121, 123, 124, 126, 128, 129, 131, 132, 133

Offset: 1

Author

Davide Rotondo, Jan 26 2025

Keywords

• nonn

Examples

			1+1+4*1*1 = 6; -2-2+4*2*2 = 12.
		

Crossrefs

Cf. A054520, A380140, A380572 (complement), A380549, A380550.

Programs

Maple

L := 150: S := {}:
for i to L do for j to L do
if 4*i*j + i + j <= L then S := `union`(S, {4*i*j+i+j}, {4*i*j+3*i+3*j+2}) fi;
od; od;
S; # Peter Bala, Jan 30 2025

Extensions

More terms from Stefano Spezia, Jan 26 2025

Missing terms 111, 121 and 126 added by Peter Bala, Jan 30 2025