A089017 n for which the number consisting of a string of n 3's and a terminal 1 is not prime.

8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 78, 79, 80, 81, 82

Offset

1,1

Comments

Complement of A055520(n)=A055557(n) - 1. The first n for which {10^(n+1) - 7}/3 is composite is thus n=8,corresponding to 333333331=17*19607843.

Links

Table of n, a(n) for n=1..70.

Mathematica

Select[Range[2, 90], !PrimeQ[FromDigits[PadLeft[{1}, #, 3]]]&]-1 (* Harvey P. Dale, Jun 19 2012 *)

Prog

(PARI) is(n)=ispseudoprime((10^(n+1)-7)/3) \\ Charles R Greathouse IV, Oct 23 2013

Crossrefs

Cf. A055520, A089018.

Sequence in context: A168098 A020722 A046037 * A182361 A023391 A115419

Adjacent sequences: A089014 A089015 A089016 * A089018 A089019 A089020

Keyword

base,nonn

Author

Lekraj Beedassy, Nov 04 2003

Status

approved