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%I #10 Jul 21 2017 13:08:36
%S 1,4,11,26,52,109,237,556,1405,3690,10085,28157,80071,230568,670122,
%T 1962690,5782468,17124206,50930440,152043592,455389240,1367883344,
%U 4119448337,12434731102,37613760490,113995567275,346090346047,1052421430209
%N Number of prime powers p^k (k != 1) <= 10^n.
%H Charles R Greathouse IV, <a href="/A076048/b076048.txt">Table of n, a(n) for n = 0..40</a>
%e a(2)=11 because 1, 4, 8, 9, 16, 25, 27, 32, 49, 64 & 81 are the only prime powers less than 100.
%t f[n_] := Block[{t = 1, k = 2}, While[s = PrimePi[10^(n/k)]; s != 0, t = t + s; k++ ]; t]; Table[ f[n], {n, 0, 27}]
%o (PARI) a(n)=my(N=10^n); sum(k=2,logint(N,2),primepi(sqrtnint(N,k)))+1 \\ _Charles R Greathouse IV_, Jul 21 2017
%Y Cf. A025475.
%K nonn
%O 0,2
%A _Robert G. Wilson v_, Oct 29 2002
%E a(16)-a(27) from _David Wasserman_, Mar 13 2005
%E a(23) corrected by _Charles R Greathouse IV_, Jul 21 2017
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