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.

1, 2, 3, 4, 6, 12, 18, 24, 28, 30, 36, 37, 40, 42, 46, 48, 49, 52, 54, 55, 60, 64, 66, 72, 78, 80, 84, 88, 90, 96, 97, 100, 102, 106, 108, 112, 114, 115, 120, 124, 126, 132, 133, 138, 144, 150, 156, 157, 160, 162, 166, 168, 172, 174, 175, 180, 184, 186, 192, 198, 200

Offset: 1

Author

Jacques Tramu, Jun 25 2008

Keywords

• nonn

Crossrefs

Cf. A140485, A140486, A140487, A140488, A140489 (second-smallest sequences).

Cf. A140490, A140491, A140492, A140493 (third-smallest sequences).

Programs

PARI

third(n) = {my(nb = 0, k = 1); while (nb != 3, if (n % k, nb++); if (nb != 3, k++);); k;}
f(n) = n + third(n);
canbe(n) = {for (k=1, n, if (k + third(k) == n, return (1));); return (0);}
cannotbe(n) = 1 - canbe(n);
lista(nn) = {for (n=1, nn, if (cannotbe(n), print1(n, ", ")););} \\ Michel Marcus, Oct 04 2018

Extensions

Corrected by Michel Marcus, Oct 04 2018