A136583 k such that floor(sqrt(10^(2*k-1))) is prime.

1, 2, 7, 18, 33, 206, 468, 1061, 6831, 40377, 47531

Offset

1,2

Comments

Number of digits of sqrt(10)-primes (A136582).

The k such that A017934(2*k-1) is prime.

Links

Table of n, a(n) for n=1..11.

Mathematica

rd = RealDigits[Sqrt[10], 10, 10^5][[1]]; Do[ If[ PrimeQ@ FromDigits@ Take[rd, n], Print@n], {n, 10^5}] (* Robert G. Wilson v, Jan 20 2008 *)

Prog

(Magma) for n in [1..10^6] do if IsPrime(Isqrt(10^(2*n-1))) then printf "%o, ", n; end if; end for; // Jason Kimberley, Sep 03 2011

Crossrefs

Cf. A010467, A017934, A017934, A131581, A132153, A136582, A175733, A175734.

Sequence in context: A107615 A195605 A184096 * A307684 A141631 A172188

Adjacent sequences: A136580 A136581 A136582 * A136584 A136585 A136586

Keyword

nonn,base,hard,more,changed

Author

Lekraj Beedassy, Jan 09 2008

Extensions

a(6)-a(8) from Robert G. Wilson v, Jan 20 2008

a(9)-a(10) from Jason Kimberley, Aug 19 and Sep 03 2011

a(11) from Michael S. Branicky, Jun 12 2026

Status

approved