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 A213606 #18 Nov 12 2019 12:50:27
%S A213606 407,1007,110207,118007,418309,429493,439099,559007,1239871,1887241,
%T A213606 2481467,2502979,3381407,3693421,5646259,6120407,6586007,6954769,
%U A213606 7042663,8350007,11305097,13083407,13760207,17297521,21159421
%N A213606 Greater of a pair (x,y) of consecutive terms of A045572 which are both semiprimes and such that the prime factors of x are adjacent primes to the factors of y.
%C A213606 Within the sequence A045572 of numbers ending in 1, 3, 7 or 9 (i.e., excluding numbers having 2 or 5 as prime factor), we look for two consecutive elements (x,y) which are both semiprimes and whose prime factors are "adjacent" primes, i.e., if x=p(i)*p(j), then we require y=p(i +/- 1)*p(j +/- 1).
%H A213606 Woodhodgson, <a href="http://groups.yahoo.com/group/primenumbers/message/24261">Adjacent composite numbers with pairs of adjacent prime factors</a>, primenumbers group, Jun 15 2012.
%H A213606 Woodhodgson, Maximilian Hasler, <a href="/A213605/a213605.txt">Adjacent composite numbers with pairs of adjacent prime factors</a>, digest of 2 messages in primenumbers Yahoo group, Jun 14 - Jun 15, 2012.
%e A213606 a(1) = 407 is the second member of the pair (403,407) which is such that 403=13*31 and 407=11*37, (11,13) and (31,37) being pairs of consecutive primes. This is the smallest pair having these properties.
%e A213606 a(2) = 1007 because (1003,1007) is the second smallest pair of consecutive numbers among those ending in 1,3,7 or 9, which are both semiprimes and such that 1003=17*59 and 1007=19*53, where (17,19) and (53,59) are pairs of consecutive primes.
%Y A213606 Cf. A213605 (the lesser ("x") of the pair of semiprimes).
%K A213606 nonn
%O A213606 1,1
%A A213606 _M. F. Hasler_, Jun 15 2012