A385654 Greatest prime factor of A385653(n).

2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 5, 5, 5, 5, 5, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 13, 13, 13, 13, 13, 7, 13, 13, 13, 13, 13, 13

Offset

1,1

Comments

A number appears in this sequence if and only if it is a uniquely popular prime; see A289662. a(n) is uniquely popular on the interval [2,A385653(n)].

Links

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

Prog

(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++); gpf(k); \\ Michel Marcus, Jul 06 2025

Crossrefs

Cf. A006530, A289662, A385503, A385652, A385653.

Sequence in context: A130255 A082527 A294235 * A186188 A227177 A387704

Adjacent sequences: A385651 A385652 A385653 * A385655 A385656 A385657

Keyword

nonn

Author

Pontus von Brömssen, Jul 06 2025

Status

approved