A240967 Numbers that end in (..., 128, 128, 128, ...) under the rule: next term = product of the last four digits in the sequence so far.

248, 418, 681, 733, 871, 1288, 1448, 1828, 2188, 2248, 2428, 2614, 2622, 2641, 2818, 3414, 3422, 3441, 3773, 4148, 4228, 4314, 4322, 4341, 4418, 4891, 4981, 6214, 6222, 6241, 6681, 6861, 7373, 7733, 7881, 8128, 8218, 8491, 8661, 8781, 8871, 8941, 9481, 9841

Offset

1,1

Comments

Additional rule: If there are fewer than k=4 digits in the sequence so far, then it is "extended to the left" with the first digit (i.e., that digit is repeated as often as necessary).

Apart from the trivial cycles (0) (cf. A239616) and (1) (entered for initial values 1 or 11 or 111 or 1111+x*10^5) and the cycle (128) considered here, the rule also allows the "constant" cycles (175) and (384), cf. A239721-A239722. These seem to be the only cycles allowed for this rule.

See A238984 for further information, including a link to Eric Angelini's SeqFan post motivating this sequence.

Links

Table of n, a(n) for n=1..44.

Prog

(PARI) is(n) = A238984(99, n, 4)==128 \\ The "99" here should be large enough to reach the cycle (128) for small initial values n. It might be necessary to increase this value in other cases.

Crossrefs

Cf. A238984, A239419, A239616, A239721, A239722.

Sequence in context: A065146 A064977 A068400 * A230856 A109478 A200426

Adjacent sequences: A240964 A240965 A240966 * A240968 A240969 A240970

Keyword

nonn,base

Author

M. F. Hasler and Bob Selcoe, Aug 05 2014

Status

approved