A131306 Smallest prime ending with exactly n identical digits.

2, 11, 1777, 23333, 199999, 2999999, 19999999, 577777777, 1777777777, 23333333333, 311111111111, 2111111111111, 17777777777777, 499999999999999, 1333333333333333, 23333333333333333, 377777777777777777, 1111111111111111111, 1111111111111111111, 911111111111111111111

Offset

1,1

Comments

By Dirichlet's theorem, there is a prime for each n. For the n in A004023, the smallest prime consists of all ones. - T. D. Noe, Oct 01 2007

Links

T. D. Noe, Table of n, a(n) for n=1..200

Example

a(4)=23333 because 23333 is the smallest prime ending with exactly 4 identical digits.

Mathematica

sp[n_]:=Module[{k=0}, While[!PrimeQ[k*10^IntegerLength[n]+n], k++]; k*10^IntegerLength[n]+n]; Join[{2}, Table[Min[sp/@FromDigits/@ Table[PadRight[{}, i, n], {n, {1, 3, 7, 9}}]], {i, 2, 20}]] (* Harvey P. Dale, Aug 28 2016; corrected by Jason Yuen, Oct 24 2025 *)

Crossrefs

Sequence in context: A051254 A095820 A101295 * A145797 A284739 A246518

Adjacent sequences: A131303 A131304 A131305 * A131307 A131308 A131309

Keyword

base,nonn

Author

Shyam Sunder Gupta, Sep 29 2007

Status

approved