This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072664 #13 Jul 16 2014 06:58:04 %S A072664 2,7,107,2187,578309,12239309,45640671719,29591195200067 %N A072664 End of smallest run of n consecutive integers with n, n-1, ..., 1 distinct prime factors in that order. %C A072664 Using a musical analogy, each run is a "crescendo" of primality where each subsequent member of the run is gradually "more prime" in the sense of having one fewer distinct prime factors (see A001221). These a(n) are the peaks of crescendos of increasing length. a(7) is greater than 60000000. %C A072664 This sequence was inspired by A068069, where the members of the runs have n different numbers of distinct prime factors, 1 through n, but where the order is not specified. %e A072664 a(1)=2 because 2 is prime and therefore the smallest integer with exactly one distinct prime factor. a(2)=7 because 6=2*3 and 7 (prime) is the smallest run of consecutive integers with exactly 2 and 1 distinct prime factors in that order. a(3)=107 because 105=3*5*7, 106=2*53 and 107 (prime) is the smallest run with exactly 3, 2 and 1 distinct prime factors in that order. Note that a(1), a(2), a(3), a(5) and a(6) are prime but that a(4)=2187=3^7 is not. %Y A072664 Cf. A086560 (smallest start with run pattern 1, 2, ..., n), A072665 (center with run pattern n+1, n, ..., 2, 1, 2, ..., n, n+1), A068069 (run order not specified), A001221 (omega(n)). %K A072664 nonn %O A072664 1,1 %A A072664 _Rick L. Shepherd_, Jun 30 2002 %E A072664 a(7) from _Donovan Johnson_, Jan 24 2009 %E A072664 a(8) from _Donovan Johnson_, Jul 19 2011