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
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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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
Comments