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 A024622 Position of 2^n among the powers of primes (A000961). 5
 1, 2, 4, 7, 11, 19, 28, 45, 71, 118, 199, 341, 605, 1079, 1962, 3591, 6636, 12371, 23151, 43580, 82268, 155922, 296348, 564689, 1078556, 2064590, 3959000, 7605135, 14632961, 28195587, 54403836, 105102702, 203287170, 393625232, 762951923, 1480223717, 2874422304 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Number of prime powers <= 2^n. - Jon E. Schoenfield, Nov 06 2016 A000961(a(n)) = A000079(n); also position of record values in A192015: A001787(n) = A192015(a(n)). - Reinhard Zumkeller, Jun 26 2011 LINKS Hiroaki Yamanouchi, Table of n, a(n) for n = 0..60 FORMULA From Ridouane Oudra, Oct 26 2020: (Start) a(n) = 1 + Sum_{i=1..n} pi(floor(2^(n/i))), where pi(n) = A000720(n); a(n) = 1 + A182908(n). (End) MATHEMATICA {1}~Join~Flatten[1 + Position[Select[Range[10^6], PrimePowerQ], k_ /; IntegerQ@ Log2@ k ]] (* Michael De Vlieger, Nov 14 2016 *) PROG (PARI) lista(nn) = {v = vector(2^nn, i, i); vpp = select(x->ispp(x), v); print1(1, ", "); for (i=1, #vpp, if ((vpp[i] % 2) == 0, print1(i, ", ")); ); } \\ Michel Marcus, Nov 17 2014 (PARI) a(n)=sum(k=1, n, primepi(sqrtnint(2^n, k)))+1 \\ Charles R Greathouse IV, Nov 21 2014 (PARI) a(n)=my(s=0); for(i=1, 2^n, isprimepower(i) && s++); s+1 \\ Dana Jacobsen, Mar 23 2021 (SAGE) def a(n): return sum(prime_pi(ZZ(2^n).nth_root(k+1, truncate_mode=1)[0]) for k in range(n))+1 # Dana Jacobsen, Mar 23 2021 (Perl) use ntheory ":all"; for my \$n (0..20) { my \$s=1; is_prime_power(\$_) && \$s++ for 1..2**\$n; print "\$n \$s\n" } # Dana Jacobsen, Mar 23 2021 (Perl) use ntheory ":all"; for my \$n (0..64) { my \$s = (\$n < 1) ? 1 : vecsum(map{prime_count(rootint(powint(2, \$n)-1, \$_))}1..\$n)+2; print "\$n \$s\n"; } # Dana Jacobsen, Mar 23 2021 (Perl with b-file for pi(2^n)) perl -Mntheory=:all -nE 'my(\$n, \$pc)=split; say "\$n ", addint(\$pc, vecsum( map{prime_count(rootint(powint(2, \$n), \$_))} 2..\$n )+1); '  b007053.txt  # Dana Jacobsen, Mar 23 2021 CROSSREFS Cf. A000961, A182908, A000720. Sequence in context: A326471 A326596 A170804 * A034337 A083024 A003292 Adjacent sequences:  A024619 A024620 A024621 * A024623 A024624 A024625 KEYWORD nonn AUTHOR EXTENSIONS a(28)-a(36) from Hiroaki Yamanouchi, Nov 21 2014 a(46)-a(53) corrected by Hiroaki Yamanouchi, Nov 15 2016 STATUS approved

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Last modified April 17 03:44 EDT 2021. Contains 343059 sequences. (Running on oeis4.)