A385653 Least k such that A385652(k) = n.

2, 4, 8, 12, 18, 24, 27, 36, 48, 54, 72, 80, 90, 100, 120, 125, 135, 150, 160, 180, 196, 210, 224, 245, 252, 280, 294, 315, 336, 343, 350, 378, 392, 420, 441, 448, 490, 504, 525, 560, 567, 588, 630, 672, 686, 700, 735, 756, 784, 840, 875, 882, 896, 945, 980

Offset: 1

Author

Pontus von Brömssen, Jul 06 2025

Keywords

• nonn

Comments

A385654(n) is uniquely popular on the interval [2,a(n)]; see A289662.

Equivalently, a(n) is the least k >= 2 such that A078899(k) = n.

Links

• Pontus von Brömssen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006530, A078899, A289662, A385503, A385652, A385654.

Programs

PARI

gpf(n) = if (n==1,1, vecmax(factor(n)[,1])); \\ A006530
f(n) = my(v=vector(n, k, gpf(k)), s=Set(v)); vecmax(apply(x->#x, vector(#s, i, select(x->(x==s[i]), v)))); \\ A385652
a(n) = my(k=2); while (f(k) !=n, k++); k; \\ Michel Marcus, Jul 06 2025