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

1,1

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).

Links

Table of n, a(n) for n=1..38.

Example

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.

Sequence in context: A304164 A379833 A199531 * A188660 A047928 A300847

Adjacent sequences: A374371 A374372 A374373 * A374375 A374376 A374377

Keyword

nonn

Author

Pontus von Brömssen, Jul 07 2024

Status

approved