decompwlj 3D

Numbers k such that k^2 + 4 is a semiprime

A242332 on the OEIS · family multiplicative

Weight–level plate of Numbers k such that k^2 + 4 is a semiprime
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 viewerA242332 on the OEIS
Terms100,000 (n = 1 … 100,000)
Decomposable (a > 2d)99,998
Level class, k > L25,209 · 25.21 %
Weight class, k ≤ L74,789 · 74.79 %
Ties, k = L63
On the level line L = 117,009
Forced level, l ≤ d²5
Range of a(n)0 … 661,675
Range of the jump d2 … 60
Largest weight k, level L661,613, 220,537

30 different gaps occur, from 2 to 60; the level share is 25.21 %; L = 1 holds 67 % 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.