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a(n) = exp(Lambda(n)), where Lambda(n) is the von Mangoldt function for odd (!) primes.
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%I #8 Jun 17 2016 00:06:11

%S 1,1,3,1,5,1,7,1,3,1,11,1,13,1,1,1,17,1,19,1,1,1,23,1,5,1,3,1,29,1,31,

%T 1,1,1,1,1,37,1,1,1,41,1,43,1,1,1,47,1,7,1,1,1,53,1,1,1,1,1,59,1,61,1,

%U 1,1,1,1,67,1,1,1,71,1,73,1,1,1,1,1,79,1,3,1,83,1,1,1,1,1,89

%N a(n) = exp(Lambda(n)), where Lambda(n) is the von Mangoldt function for odd (!) primes.

%C a(n) = p if n = p^k and p odd prime, k >= 1, otherwise 1.

%D Tom M. Apostol, Introduction to analytic number theory, Springer-Verlag, 1976.

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Von_Mangoldt_function">Von Mangoldt function</a>

%F a(n) = 1 + Sum_{k=3..n} (k-1)*A010051(k)*(floor(k^n/n)-floor((k^n -1)/n)). - _Anthony Browne_, Jun 16 2016

%e a(8) = 1 because 8 = 2^3 is not the power of an odd prime, a(49) = 7 because 49 = 7^2.

%p a := proc(n) local lcm; lcm := n -> ilcm(seq(i,i = 1..n)); if type(n,even) then 1 else lcm(n)/lcm(n-1) fi end;

%t a[n_] := If[IntegerQ[Log[2, n]], 1, Exp[MangoldtLambda[n]]]; Table[a[n], {n, 1, 89}] (* _Jean-François Alcover_, Jan 27 2014 *)

%Y Cf. A014963.

%K nonn

%O 1,3

%A _Peter Luschny_, Jan 22 2009, Jan 25 2009