decompwlj 3D

Heptagonal numbers (or 7-gonal numbers): n*(5*n-3)/2

A000566 on the OEIS · family polynomial · also known as Heptagonal numbers

Weight–level plate of Heptagonal numbers (or 7-gonal numbers): n*(5*n-3)/2
Click the plate to explore it in 3-D. Weight k across, level L up, both on log scales: blue in the weight class (k ≤ L), orange in the level class (k > L). The dashed diagonal is k = L.
Open in the 3-D viewerA000566 on the OEIS
Terms100,000 (n = 0 … 99,999)
Decomposable (a > 2d)99,995
Level class, k > L99,995 · 100.00 %
Weight class, k ≤ L0 · 0.00 %
Ties, k = L0
On the level line L = 110,138
Forced level, l ≤ d²99,995
Range of a(n)0 … 24,999,350,004
Range of the jump d1 … 499,996
Largest weight k, level L24,995,850,167, 49,627

n(5n - 3)/2. For a ~ c n^2, l/d^2 -> 1/(4c); here c = 5/2, so l <= d^2 and every decomposable term is forced level (100 %), as for the squares and pentagonal numbers.

The decomposition

Every term of a strictly increasing sequence is written a(n) = k(n)·L(n) + d(n): the jump d = a(n+1) − a(n), the weight k the least divisor of a − d greater than d, the level L = (a − d)/k. A term decomposes when a > 2d; it is in the level class when k > L and in the weight class when k ≤ L. See decompwlj.com and arXiv:0711.0865, or how it works, with worked examples and a live one.