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 A231816 #11 Nov 18 2013 16:37:07 %S A231816 2,6,30,351137972965951,8596208716179446431, %T A231816 698211042943963834650959743951,744014385572130806167897354113929551, %U A231816 901203402294977554329263775346819632824908852456695769189267773301 %N A231816 a(n) = the smallest squarefree number (A005117) with n prime factors in a 2p-1 progression. %C A231816 Smallest squarefree numbers with n >= 2 prime divisors of the form p_1 * p_2 * … * p_n, where p_1 < p_2 < … < p_k = primes with p_k = 2 * p_(k-1) - 1. %C A231816 Subsequence of A231814. %H A231816 Jaroslav Krizek, <a href="/A231816/b231816.txt">Table of n, a(n) for n = 1..15</a> %e A231816 8596208716179446431 = 1531*3061*6121*12241*24481, where 3061 = 2*1531 - 1, 6121 = 2*3061 - 1, 12241 = 2*6121 - 1, 24481 = 2*12241 - 1. %Y A231816 Cf. A005117, A000040, A231814, A231815. %Y A231816 Cf. A057330 (first prime for such numbers that has n factors). %K A231816 nonn %O A231816 1,1 %A A231816 _Jaroslav Krizek_, Nov 13 2013