decompwlj 3D

Primes p with p-1 and p+1 both practical: "Sandwich of the first kind"

A210479 on the OEIS · family primes

Weight–level plate of Primes p with p-1 and p+1 both practical: "Sandwich of the first kind"
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 viewerA210479 on the OEIS
Terms100,000 (n = 1 … 100,000)
Decomposable (a > 2d)99,995
Level class, k > L54,509 · 54.51 %
Weight class, k ≤ L45,486 · 45.49 %
Ties, k = L1
On the level line L = 18,285
Forced level, l ≤ d²1,737
Range of a(n)3 … 108,199,639
Range of the jump d2 … 11,928
Largest weight k, level L108,182,623, 36,012,713

1,650 different gaps occur, from 2 to 11,928; the level share is 54.51 %; 1.7 % of terms are forced level (l <= d^2).

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.