A136582 Sqrt(10)-primes: primes obtained by concatenating the first digits in the decimal expansion of sqrt(10).

3, 31, 3162277, 316227766016837933, 316227766016837933199889354443271

Offset: 1

Author

Lekraj Beedassy, Jan 09 2008

Keywords

• nonn
• base

Comments

n such that floor(sqrt(10^(2*n-1))) is prime (1, 2, 7, 18, 33, ...) are given in A136583.

This sequence is the list of prime terms in A017934.

The next term has 206 digits. - Harvey P. Dale, Dec 06 2023

Crossrefs

Cf. A010467, A017934, A017934, A131581, A132153, A136583, A175733, A175734.

Programs

Magma

// by Jason Kimberley, Aug 2011
for n in [1..499 by 2] do
  f := Isqrt(10^n);
  if IsPrime(f) then
    printf "%o,", f;
  end if;
end for;

Mathematica

Module[{nn=50,sq10},sq10=RealDigits[Sqrt[10],10,nn][[1]];Select[FromDigits/@Table[Take[sq10,n],{n,nn}],PrimeQ]] (* Harvey P. Dale, Dec 06 2023 *)

Formula

a(n) = A017934(2*A136583(n)-1).