A355854 Numbers of the form (ab+cd)*(ad+bc) with integers a,b,c,d >= 1.

4, 9, 16, 20, 25, 35, 36, 49, 54, 56, 60, 64, 77, 80, 81, 91, 99, 100, 104, 108, 110, 121, 128, 135, 136, 140, 143, 144, 154, 156, 169, 170, 171, 176, 180, 182, 187, 189, 195, 196, 209, 216, 220, 221, 224, 225, 240, 250, 252, 256, 260, 266, 270, 272, 275, 286, 289

Offset: 1

Author

Thomas Kerscher, Jul 30 2022

Keywords

• nonn

Examples

			77 is in the sequence because (1*1+2*5)(1*5+1*2)=77 (for a=1, b=1, c=2, d=5).
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000290.

Extensions

More terms from David A. Corneth, Jul 30 2022