decompwlj 3D

Numbers n such that d(d(n)) is an odd prime, where d(k) is the number of divisors of k

A036455 on the OEIS · family divisor functions

Weight–level plate of Numbers n such that d(d(n)) is an odd prime, where d(k) is the number of divisors of k
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 viewerA036455 on the OEIS
Terms100,000 (n = 1 … 100,000)
Decomposable (a > 2d)100,000
Level class, k > L14,205 · 14.21 %
Weight class, k ≤ L85,795 · 85.80 %
Ties, k = L45
On the level line L = 19,927
Forced level, l ≤ d²5
Range of a(n)6 … 290,319
Range of the jump d1 … 28
Largest weight k, level L290,317, 145,154

26 different gaps occur, from 1 to 28; the level share is 14.21 %; L = 1 holds 70 % of the level class.

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.