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 A173617 Numbers n such that phi(tau(n))= rad(n) 0
 1, 4, 8, 32, 36, 192, 288, 768, 972, 1458, 5120, 13122, 326592, 19531250, 22588608, 46137344, 171532242 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS rad(n) is the product of the primes dividing n (A007947 ) tau(n) is the number of divisors of n (A000005) phi(n): Euler totient function (A000010) a(18) > 10^10. - Donovan Johnson, Jul 27 2011 REFERENCES M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840. LINKS P. A. MacMahon, Divisors of numbers and their continuations in the theory of partitions, Proc. London Math. Soc., 19 (1919), 75-113. W. Sierpinski, Number Of Divisors And Their Sum, Elementary theory of numbers, Warszawa, 1964. Wikipedia, Euler's totient function FORMULA n such that A163109(n)= A007947(n) EXAMPLE tau(8) = 4, phi(4)=2 and rad(8)=2 tau(13122) = 18, phi(18)=6 and rad(13122)=6 MAPLE with(numtheory):for n from 1 to 1000000 do :t1:= ifactors(n)[2] : t2 :=mul(t1[i][1], i=1..nops(t1)): if phi(tau(n)) = t2 then print (n): else fi : od : CROSSREFS Cf. A173320, A062069, A001414, A001222. Sequence in context: A129195 A180098 A124143 * A034041 A050442 A229953 Adjacent sequences:  A173614 A173615 A173616 * A173618 A173619 A173620 KEYWORD nonn,changed AUTHOR Michel Lagneau, Feb 22 2010 EXTENSIONS a(14)-a(17) from Donovan Johnson, Jul 27 2011 STATUS approved

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Last modified July 23 16:14 EDT 2019. Contains 325258 sequences. (Running on oeis4.)