cp's OEIS Frontend

A227974 Minimum composite squarefree numbers k such that p(i)+n divides k-n, for n=1, 2, 3, 4,..., where p(i) are the prime factors of k .

%I A227974 #11 Jun 16 2016 21:54:22
%S A227974 385,182,195,1054,165,6,1015,4958,2193,10,5159,113937,5593,14,15,
%T A227974 196009,3657,6318638,2755,1227818,21,22,2795,152358,12121,26,21827,
%U A227974 17578,36569,30,38335,457907,33,34,35
%N A227974 Minimum composite squarefree numbers k such that p(i)+n divides k-n, for n=1, 2, 3, 4,..., where p(i) are the prime factors of k .
%C A227974 Fixed points are the squarefree semiprimes.
%e A227974 For n=3 the minimum k is 195. Prime factors of 195 are 3, 5 and 13. We have: 195 - 3 = 192, 3 + 3 = 6 and 192 / 6 = 32, 5 + 3 = 8 and 192 / 8 = 24, 13 + 3 = 16 and 192 / 16 = 12.
%p A227974 with(numtheory); P:=proc(i) local c, d, k, n, ok, p; for k from 1 to i do
%p A227974 for n from 2 to i do if not isprime(n) then p:=ifactors(n)[2]; ok:=1;
%p A227974 for d from 1 to nops(p) do if p[d][2]>1 then ok:=0; break; fi;
%p A227974 if  not type((n-k)/(p[d][1]+k), integer) then ok:=0; break; fi; od;
%p A227974 if ok=1 then print(n); break; fi; fi; od; od; end: P(10^6);
%Y A227974 Cf. A208728, A225702-A225720, A227973, A227976.
%K A227974 nonn
%O A227974 1,1
%A A227974 _Paolo P. Lava_, Aug 02 2013