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

Author

Amarnath Murthy, Nov 25 2003

Keywords

• base
• nonn

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).

Crossrefs

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

Programs

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 *)

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

Extensions

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

Extended by Eduard Roure Perdices, Apr 18 2021