Voozh

A114125

a(n) is the 10^n-th semiprime.

4, 26, 314, 3595, 40882, 459577, 5109839, 56168169, 611720495, 6609454805, 70937808071, 757060825018, 8040423200947, 85037651263063, 896113850117314, 9413000361625346, 98597629032410971, 1030179406403917981, 10739422018595513973, 111729397883168684917, 1160260967837159869621

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OFFSET

0,1

LINKS

Table of n, a(n) for n=0..20.

Eric Weisstein's World of Mathematics, Semiprime.

MATHEMATICA

fQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; c = 0; k = 2; Do[While[c < 10^n, If[fQ@k, c++ ]; k++ ]; Print[k - 1], {n, 0, 8}]

(* checked by *) SemiPrimePi[n_] := Sum[ PrimePi[n/Prime@i] - i + 1, {i, PrimePi@ Sqrt@n}]

PROG

(Perl) use ntheory ":all"; print "$_ ", nth_semiprime(10**$_), "\n" for 0..15; # Dana Jacobsen, Oct 08 2018

CROSSREFS