A288847 - OEIS

A288847

Numbers whose trajectories under the map x -> A230625(x) never reach a prime.

217, 255, 446, 558, 717, 735, 775, 945, 958, 1007, 1062, 1115, 1269, 1344, 1503, 1984, 2215, 2358, 3003, 3751, 3858, 4131, 4471, 5144, 6174, 6627, 6915, 6923, 7033, 7073, 7139, 7434, 7530, 7778, 8125, 8142, 8239, 8335, 8575, 8967, 9186, 9303, 10040, 10179, 10856, 11907, 12081, 12248

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Sequence suggested by N. J. A. Sloane on the SeqFan mailing list. These are also the numbers n for which A230626(n) = -1 and A230627(n) = A287875(n) = 0. All currently-listed terms (those <= 3858) enter one of the two loops 1007 <-> 1269 and 1503 <-> 3751.

Further values added (Jun 19 2017) based on Sean A. Irvine's extension of the b-file for A230626.

LINKS

Table of n, a(n) for n=1..48.

EXAMPLE

217, 255, 945, 1007 and 1269 are in the sequence because under the map x -> A230625(x):

217 = 7*31 = binary 111*11111 -> binary 11111111 = 255

255 = 3*5*17 = binary 11*101*10001 -> binary 1110110001 = 945

945 = 3^3*5*7 = binary 11^11*101*111 -> binary 1111101111 = 1007

1007 = 19*53 = binary 10011*110101 -> binary 10011110101 = 1269

1269 = 3^3*47 = binary 11^11*101111 -> binary 1111101111 = 1007

CROSSREFS

Cf. A230625, A230626, A230627, A287874, A287875, A287878.