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A064489 a(n) is the smallest number m such that prime(m) has prime(n) decimal digits.

%I A064489 #30 Sep 03 2024 08:25:07
%S A064489 5,26,1230,78499,455052512,37607912019,279238341033926,
%T A064489 24739954287740861,201467286689315906291,157589269275973410412739599
%N A064489 a(n) is the smallest number m such that prime(m) has prime(n) decimal digits.
%F A064489 a(n) = 1 + A006880(A000040(n)-1). [Corrected by _Amiram Eldar_, Sep 03 2024]
%F A064489 a(n) = A000720(A064490(n)).
%e A064489 For n = 1: a(1) = 5 because prime(5) = 11 is the first prime with 2 = prime(1) decimal digits.
%o A064489 (PARI) l(n)=ln=0; while(n,n=floor(n/10); ln++); return(ln);
%o A064489 a=0; for(n=1,10^6,x=l(prime(n)); if(isprime(x),b=x; if(b>a,a=b; print1(n, ", "))))
%o A064489 (Python)
%o A064489 from sympy import prime, nextprime, primepi
%o A064489 def a(n): return primepi(nextprime(10**(prime(n)-1)))
%o A064489 print([a(n) for n in range(1, 6)]) # _Michael S. Branicky_, May 26 2021
%Y A064489 Cf. A000040, A000720, A006880, A064490.
%K A064489 base,nonn,hard,more
%O A064489 1,1
%A A064489 _Jason Earls_, Oct 04 2001
%E A064489 More terms from _David Wasserman_, Jul 22 2002
%E A064489 a(10) from the b-file at A006880 added by _Amiram Eldar_, Sep 03 2024