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URL: https://oeis.org/A385654

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A385654
Greatest prime factor of A385653(n).
3
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
KEYWORD
nonn
AUTHOR
STATUS
approved