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 A120317 #2 Mar 30 2012 18:36:04 %S A120317 6080399213078595601,106451203123324908289,842122675409157900289, %T A120317 205035001401532317649921,690310240598397005456401, %U A120317 1125500133125681400538801,1241419580861102113344769 %N A120317 Consecutive refactorable numbers a(n)-1, a(n) in which 7 the smallest prime divisor of a(n). %F A120317 a(n) is the first integer of the form (7*k)^(7-1) such that both a(n) and a(n)-1 is refactorable and 7 is the smallest prime divisor of a(n). %p A120317 with(numtheory); RFC7:=[]: p:=ithprime(4): P:=[seq(ithprime(i),i=1..3)]; for w to 1 do for k from 3 to 12^4 by 2 do if andmap(z -> k mod z <> 0, P) then m:=p*k; n:=m^(p-1); t:=tau(n); n1:=n-1; t1:=tau(n1); if (n mod t = 0) and (n1 mod t1 = 0) then RFC7:=[op(RFC7),n]; print(ifactor(n)); fi fi; od od; %Y A120317 Cf. A033950, A036898, A114617. %K A120317 nonn %O A120317 1,1 %A A120317 _Walter Kehowski_, Jun 20 2006