decompwlj 3D

Numbers whose iterated sum of digits is a prime

A028835 on the OEIS · family digit rule

Weight–level plate of Numbers whose iterated sum of digits is a prime
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 viewerA028835 on the OEIS
Terms100,000 (n = 1 … 100,000)
Decomposable (a > 2d)99,997
Level class, k > L12,163 · 12.16 %
Weight class, k ≤ L87,834 · 87.84 %
Ties, k = L54
On the level line L = 16,701
Forced level, l ≤ d²2
Range of a(n)2 … 224,998
Range of the jump d1 … 4
Largest weight k, level L224,947, 112,496

The gaps are 1, 2 and 4; the level share is 12.16 %; L = 1 holds 55 % 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.