A064489 a(n) = smallest m such that prime(m) has prime(n) decimal digits.

5, 26, 1230, 78499, 455052512, 37607912019, 279238341033926, 24739954287740861, 201467286689315906291

Offset

1,1

Links

Table of n, a(n) for n=1..9.

Formula

a(n) = 1 + A006880(A000040(n-1)) for n > 1.

a(n) = A000720(A064490(n)).

Example

n=1: prime(5) = 11 is the first prime with 2 = prime(1) decimal digits.

Prog

(PARI) l(n)=ln=0; while(n, n=floor(n/10); ln++); return(ln);
a=0; for(n=1, 10^6, x=l(prime(n)); if(isprime(x), b=x; if(b>a, a=b; print1(n, ", "))))
(Python)
from sympy import prime, nextprime, primepi
def a(n): return primepi(nextprime(10**(prime(n)-1)))
print([a(n) for n in range(1, 6)]) # Michael S. Branicky, May 26 2021

Crossrefs

Cf. A000040, A000720, A006880, A064490.

Sequence in context: A226125 A132509 A281747 * A081089 A180928 A366332

Adjacent sequences: A064486 A064487 A064488 * A064490 A064491 A064492

Keyword

base,nonn,hard,more

Author

Jason Earls, Oct 04 2001

Extensions

More terms from David Wasserman, Jul 22 2002

Status

approved