A090226 Least k such that prime(k) has n digits. Index of least n-digit prime.

1, 5, 26, 169, 1230, 9593, 78499, 664580, 5761456, 50847535, 455052512, 4118054814, 37607912019, 346065536840, 3204941750803, 29844570422670, 279238341033926, 2623557157654234, 24739954287740861, 234057667276344608, 2220819602560918841, 21127269486018731929

Offset

1,2

Links

Eduard Roure Perdices, Table of n, a(n) for n = 1..29

C. Caldwell's Prime Pages, A Table of values of pi(x).

X. Gourdon, A Table of values of pi(x).

Formula

a(1)=1; a(n) = pi(10^(n-1)) + 1 for n > 1 where pi(x) is the number of primes less than x. - C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 26 2004

a(n) = A006880(n-1) + 1, for n >= 1. - Eduard Roure Perdices, Apr 18 2021

Mathematica

Table[PrimePi[NextPrime[10^n]], {n, 0, 14}] (* This generates the first 15 terms of the sequence, but Mathematica cannot generate the 16th term using this program. *) (* Harvey P. Dale, May 12 2019 *)

Crossrefs

Cf. A003617 (values of prime(k)), A006880.

Sequence in context: A209672 A367041 A057793 * A355672 A356597 A094422

Adjacent sequences: A090223 A090224 A090225 * A090227 A090228 A090229

Keyword

base,nonn

Author

Amarnath Murthy, Nov 25 2003

Extensions

Corrected and extended by C. Ronaldo (aga_new_ac(AT)hotmail.com), Dec 26 2004

Extended by Eduard Roure Perdices, Apr 18 2021

Status

approved