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A076048 Number of prime powers p^k (k != 1) <= 10^n. 4
1, 4, 11, 26, 52, 109, 237, 556, 1405, 3690, 10085, 28157, 80071, 230568, 670122, 1962690, 5782468, 17124206, 50930440, 152043592, 455389240, 1367883344, 4119448337, 12434731102, 37613760490, 113995567275, 346090346047, 1052421430209 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 0..40

EXAMPLE

a(2)=11 because 1, 4, 8, 9, 16, 25, 27, 32, 49, 64 & 81 are the only prime powers less than 100.

MATHEMATICA

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}]

PROG

(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

CROSSREFS

Cf. A025475.

Sequence in context: A159944 A002763 A077270 * A109414 A027966 A141534

Adjacent sequences:  A076045 A076046 A076047 * A076049 A076050 A076051

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Oct 29 2002

EXTENSIONS

a(16)-a(27) from David Wasserman, Mar 13 2005

a(23) corrected by Charles R Greathouse IV, Jul 21 2017

STATUS

approved

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Last modified February 21 04:22 EST 2018. Contains 299389 sequences. (Running on oeis4.)