A105427 Numbers n such that the near-repdigit number consisting of a 1 followed by n 3's (i.e., of form 1333...33) is composite.

2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 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

Offset

1,1

Comments

Complement of A056698.

Links

Table of n, a(n) for n=1..72.

FactorDB, Factorizations of (10^n-1)/3+10^n

Makoto Kamada, Factorizations of 133...33.

Mathematica

Select[Range[100], CompositeQ[FromDigits[PadRight[{1}, #, 3]]]&]-1 (* Harvey P. Dale, Jul 23 2014 *)

Prog

(PARI) isok(n) = ! isprime(10^n+(10^n-1)/3) \\ Michel Marcus, Jul 28 2013

Crossrefs

Cf. A051200, A089017, A093671.

Sequence in context: A161953 A187829 A356974 * A247160 A023808 A331995

Adjacent sequences: A105424 A105425 A105426 * A105428 A105429 A105430

Keyword

nonn

Author

Lekraj Beedassy, Apr 08 2005

Status

approved