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A064394 Exponent of highest power of 2 dividing n! equals the largest prime < n. 3

%I

%S 4,5,8,9,22,23,26,27,32,33,50,51,56,57,70,71,76,77,82,83,94,95,100,

%T 101,112,113,118,119,128,129,134,135,176,177,186,187,196,197,266,267,

%U 274,275,280,281,296,297,342,343,352,353,358,359,364,365,372,373,386,387

%N Exponent of highest power of 2 dividing n! equals the largest prime < n.

%C [n/2]+[n/4]+[n/8]+[n/16]+... = prevprime(n).

%H Harvey P. Dale, <a href="/A064394/b064394.txt">Table of n, a(n) for n = 0..1000</a>

%e 8!=2^7*3^2*5*7, 23!=2^19*3^9*5^4*7^3*11^2*13*17*19*23.

%p for n from 3 to 10^3 do if sum(floor(n/(2^i)), i=1..15) = prevprime(n) then printf(`%d,`,n) fi; od:

%t Select[Range[400],IntegerExponent[#!,2]==NextPrime[#,-1]&] (* _Harvey P. Dale_, Sep 24 2013 *)

%Y Cf. A011371, A007917.

%K nonn

%O 0,1

%A _Vladeta Jovovic_, Sep 29 2001

%E More terms from _James A. Sellers_, Oct 01 2001

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Last modified November 11 18:50 EST 2019. Contains 329031 sequences. (Running on oeis4.)