cp's OEIS Frontend

A140494 Numbers that cannot be part of the trajectory of any number under repeated application of the map: n -> n + third-smallest number that does not divide n, unless they are the first term of the trajectory.

%I A140494 #20 Oct 08 2018 04:15:05
%S A140494 1,2,3,4,6,12,18,24,28,30,36,37,40,42,46,48,49,52,54,55,60,64,66,72,
%T A140494 78,80,84,88,90,96,97,100,102,106,108,112,114,115,120,124,126,132,133,
%U A140494 138,144,150,156,157,160,162,166,168,172,174,175,180,184,186,192,198,200
%N A140494 Numbers that cannot be part of the trajectory of any number under repeated application of the map: n -> n + third-smallest number that does not divide n, unless they are the first term of the trajectory.
%o A140494 (PARI) third(n) = {my(nb = 0, k = 1); while (nb != 3, if (n % k, nb++); if (nb != 3, k++);); k;}
%o A140494 f(n) = n + third(n);
%o A140494 canbe(n) = {for (k=1, n, if (k + third(k) == n, return (1));); return (0);}
%o A140494 cannotbe(n) = 1 - canbe(n);
%o A140494 lista(nn) = {for (n=1, nn, if (cannotbe(n), print1(n, ", ")););} \\ _Michel Marcus_, Oct 04 2018
%Y A140494 Cf. A140485, A140486, A140487, A140488, A140489 (second-smallest sequences).
%Y A140494 Cf. A140490, A140491, A140492, A140493 (third-smallest sequences).
%K A140494 nonn
%O A140494 1,2
%A A140494 _Jacques Tramu_, Jun 25 2008
%E A140494 Corrected by _Michel Marcus_, Oct 04 2018