A384014 a(n) is the number of n-digit terms in A384013.

0, 1, 16, 108, 834, 6893, 58659, 510839, 4515301, 40477023, 366751460, 3352789726, 30877698604, 286159371452, 2666303391801, 24959756192476, 234610874384116, 2213224276178123, 20945897352118544, 198802912201260034, 1891788092230264832, 18044365524165259927, 172479703095316537972

Offset

1,3

Links

Table of n, a(n) for n=1..23.

Tomás Oliveira e Silva, Tables of values of pi(x) and of pi2(x)

Mathematica

a[1]:=0; a[n_]:=Module[{count=0}, For[k=Prime[PrimePi[10^(n-1)]+1], k<=Prime[PrimePi[10^n-1]], k=NextPrime[k], If[Part[d=IntegerDigits[k], 1]==Part[d, 2], count++]]; count]; Array[a, 7]

Crossrefs

Cf. A383979, A384013, A384016.

Sequence in context: A163725 A269188 A165558 * A337391 A250425 A238171

Adjacent sequences: A384011 A384012 A384013 * A384015 A384016 A384017

Keyword

nonn,base

Author

Stefano Spezia, May 17 2025

Extensions

a(11)-a(23) from David Radcliffe, May 17 2025

Status

approved