A374374 Oblong numbers that are products of smaller oblong numbers.

12, 72, 240, 420, 600, 1056, 1260, 2352, 4032, 6480, 7140, 9120, 9900, 10920, 14280, 14520, 18360, 20592, 20880, 28392, 38220, 46872, 50400, 65280, 78120, 82656, 83232, 104652, 123552, 129960, 147840, 159600, 194040, 233772, 245520, 262656, 278256, 279312

Offset: 1

Author

Pontus von Brömssen, Jul 07 2024

Keywords

• nonn

Comments

The oblong number (k^2+2*k)*(k^2+2*k+1) = A047928(k+2) is a term for all k >= 1, because it is the product of the oblong numbers k*(k+1) and (k+1)*(k+2).

Examples

			72 is a term because 72 = 8*9 = 6*12 = (2*3)*(3*4).
1056 is a term because 1056 = 32*33 = 2*2*2*132 = (1*2)*(1*2)*(1*2)*(11*12). (This is the first term that requires more than two factors.)
		

Crossrefs

A188660 is a subsequence (only 2 factors allowed).

Cf. A002378, A047928, A068143, A374375.