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 A173334 Numbers n such that tau(phi(n))= phi(sum-of-prime-divisors(n)). 0
 2, 3, 15, 18, 24, 28, 30, 33, 39, 50, 52, 55, 80, 132, 133, 152, 169, 186, 187, 190, 195, 207, 215, 217, 222, 230, 238, 247, 261, 266, 305, 319, 333, 340, 352, 369, 371, 414, 481, 484, 494, 496, 497, 506, 516, 522, 559, 574, 580, 611, 644, 646, 660, 671, 689 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that A000005(A000010(n)) = A000010(A008472(n)). 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 (1921), 75-113. W. Sierpinski, Number Of Divisors And Their Sum, Monogr. Matemat. 42 (1964) chapter IV Wikipedia, Euler's totient function FORMULA {n : A062821(n)= phi(A008472(n))}. EXAMPLE For n=15, tau(phi(15)) = tau(8)=4 equals phi(A008472(15))=phi(8) = 4, which adds 15 to the sequence. For n=18, tau(phi(18)) = tau(6) =4 equals phi(A008472(18)) = phi(5) = 4, which adds 18 to the sequence. MAPLE with(numtheory): for n from 1 to 1800 do : t1:= ifactors(n)[2] : t2 :=sum(t1[i][1], i=1..nops(t1)):if tau(phi(n)) = phi(t2) then print (n): else fi : od : MATHEMATICA Select[Range[2, 700], DivisorSigma[0, EulerPhi[#]] == EulerPhi[Total[FactorInteger[#][[All, 1]]]] &] (* Jean-François Alcover, May 19 2011 *) CROSSREFS Sequence in context: A066491 A282383 A299486 * A294131 A274003 A101507 Adjacent sequences:  A173331 A173332 A173333 * A173335 A173336 A173337 KEYWORD nonn AUTHOR Michel Lagneau, Feb 16 2010 EXTENSIONS Removed sopf acronym. Updated references and links - R. J. Mathar, Mar 10 2010 STATUS approved

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Last modified February 21 15:34 EST 2019. Contains 320374 sequences. (Running on oeis4.)