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%I #6 Jan 01 2019 16:31:44
%S 38604666779024731098340977806401,7208577773559712596404976530284801,
%T 695314235787112476661749457231833601,
%U 313468146036745542621075945985861000534849
%N Consecutive refactorable numbers a(n)-1, a(n) in which 11 is the smallest prime divisor of a(n).
%F a(n) is the first integer of the form (11*k)^(11-1) such that both a(n) and a(n)-1 is refactorable and 11 is the smallest prime divisor of a(n).
%p with(numtheory); RFC11:=[]: p:=ithprime(5): P:=[seq(ithprime(i),i=1..4)]; 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 RFC11:=[op(RFC11),n]; print(ifactor(n)); fi fi; od od;
%Y Cf. A033950, A036898, A114617.
%K nonn
%O 1,1
%A _Walter Kehowski_, Jun 20 2006