

A267422


Largest prime factor of the largest squarefree practical number comprising n prime factors.


0




OFFSET

1,1


COMMENTS

Note that the prime factors of the largest squarefree practical number with n prime factors are the first n members of a(n). The largest squarefree practical number with 3 prime factors is 78 = 2*3*13 and the largest squarefree practical number with 5 prime factors is 367580694 = 2*3*13*167*28219, etc.


LINKS

Table of n, a(n) for n=1..9.
Wikipedia, Practical number and Squarefree integer


EXAMPLE

a(3) = 13 because there are only 4 squarefree practical numbers with 3 prime factors, namely 2*3*5 = 30, 2*3*7 = 42, 2*3*11 = 66 and 2*3*13 = 78. So 78 is the largest squarefree practical number with 3 prime factors and the largest prime factor is 13.


MATHEMATICA

lst={2}; Do[If[PrimeQ[f=DivisorSigma[1, Apply[Times, lst]]+1], AppendTo[lst, f], AppendTo[lst, NextPrime[f, 1]]], {8}]; lst


CROSSREFS

Cf. A005117, A005153, A265501.
Sequence in context: A153888 A068083 A137459 * A072162 A113785 A118323
Adjacent sequences: A267419 A267420 A267421 * A267423 A267424 A267425


KEYWORD

nonn,more


AUTHOR

Frank M Jackson, Jan 14 2016


STATUS

approved



