A268702 Largest n digit prime having at least n-1 digits equal to 1.

7, 71, 911, 8111, 16111, 911111, 1171111, 71111111, 131111111, 1711111111, 31111111111, 311111111111, 5111111111111, 41111111111111, 111151111111111, 5111111111111111, 11111611111111111, 191111111111111111, 2111111111111111111, 11111111611111111111

Offset

1,1

Links

Michel Lagneau, Michael De Vlieger and Robert G. Wilson v, Table of n, a(n) for n = 1..1000

Example

a(3) = 911 since 111, 211, 311, ..., 811 are all composites but 911 is prime. Also of the ten primes of 3 digits which contain at least 2 ones, {101, 113, 131, 151, 181, 191, 211, 311, 811, 911}, 911 is the greatest.

Mathematica

f[n_] := Block[{k = 0, p = {}, r = (10^n - 1)/9, s = Range@ 10 - 2}, While[k < n, AppendTo[p, Select[r + 10^k*s, PrimeQ]]; k++]; p = Max@ Flatten@ p]; Array[f, 20]

Prog

(PARI) a(n) = {p = precprime(10^n-1); while (#select(x->x==1, digits(p)) != n-1, p = precprime(p-1)); p; } \\ Michel Marcus, Feb 21 2016

Crossrefs

Cf. A177999, A241100, A268703 - A268707, A241206.

Sequence in context: A067307 A334135 A357155 * A363009 A052390 A002119

Adjacent sequences: A268699 A268700 A268701 * A268703 A268704 A268705

Keyword

nonn,base

Author

Michel Lagneau, Michael De Vlieger and Robert G. Wilson v, Feb 11 2016

Status

approved