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

Author

Lekraj Beedassy, Apr 08 2005

Keywords

• nonn
• base

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

Crossrefs

Cf. A098406, A105433.

Programs

Mathematica

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

PARI

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