A105432 Numbers n such that the near-repdigit number consisting of n-1 1's followed by a terminal 3 (i.e., of the form 111...1113) is composite.

4, 6, 7, 8, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78

Offset

1,1

Comments

Complement of A097683.

Numbers k such that (10^n + 17)/9 is composite (see A098406).

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

IntegerLength/@Select[Table[FromDigits[PadLeft[{3}, n, 1]], {n, 80}], CompositeQ] (* Harvey P. Dale, Feb 05 2025 *)

Prog

(PARI) isok(n) = ! isprime((10^n + 17)/9); \\ Michel Marcus, Jul 27 2017

Crossrefs

Cf. A098406, A105433.

Sequence in context: A225551 A247359 A305415 * A324704 A203168 A284820

Adjacent sequences: A105429 A105430 A105431 * A105433 A105434 A105435

Keyword

nonn,base

Author

Lekraj Beedassy, Apr 08 2005

Status

approved