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a(n) is the first term in a chain of at least n consecutive numbers each with exactly 7 distinct prime factors.
4

%I #11 Jul 17 2017 10:36:10

%S 510510,965009045,30989984674,1673602584618

%N a(n) is the first term in a chain of at least n consecutive numbers each with exactly 7 distinct prime factors.

%C a(5) > 10^13.

%H Roger B. Eggleton and James A. MacDougall, <a href="http://www.jstor.org/stable/27643119">Consecutive integers with equally many principal divisors</a>, Math. Mag. 81 (2008), 235-248. [_T. D. Noe_, Oct 13 2008]

%Y Cf. A087977, A087978, A138206, A154573.

%K nonn,more

%O 1,1

%A _Donovan Johnson_, Mar 06 2008

%E a(4) from _Donovan Johnson_, Jan 15 2009