Search: id:A002181
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%I A002181 M2421 N0957
%S A002181 0,3,5,7,15,11,13,17,19,25,23,35,29,31,51,37,41,43,69,47,65,53,81,87,59,
%T A002181 61,85,67,71,73,79,123,83,129,89,141,97,101,103,159,107,109,121,113,177,
%U A002181 143,127,255,131,161,137,139,213,185,149,151,157,187,163,249,167,203,173
%N A002181 Least number k such that phi(k) = n, where n runs through the values 
               (A002202) taken by phi.
%C A002181 Inverse of Euler totient function.
%C A002181 A051445 without the zeros. The values of n are in A002180.
%C A002181 According to Guy, the first even term is for 2n=16842752=257*2^16. If 
               there are only five Fermat primes, then terms will be even for 2n=2^r 
               for all r>31. This was discussed in problem E3361. [From T. D. Noe 
               (noe(AT)sspectra.com), Aug 14 2008]
%D A002181 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002181 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002181 J. W. L. Glaisher, Number-Divisor Tables. British Assoc. Math. Tables, 
               Vol. 8, Camb. Univ. Press, 1940, p. 64.
%D A002181 R. K. Guy, Unsolved problems in number theory, B39. [From T. D. Noe (noe(AT)sspectra.com), 
               Aug 14 2008]
%D A002181 William P. Wardlaw, L. L. Foster and R. J. Simpson, Problem E3361, Amer. 
               Math. Monthly, Vol. 98, No. 5 (May, 1991), 443-444. [From T. D. Noe 
               (noe(AT)sspectra.com), Aug 14 2008]
%H A002181 T. D. Noe, <a href="b002181.txt">Table of n, a(n) for n=1..10000</a>
%H A002181 T. D. Noe, <a href="http://www.sspectra.com/math/16842752.txt">Numbers 
               Like 16842752</a> [From T. D. Noe (noe(AT)sspectra.com), Aug 19 2008]
%Y A002181 Cf. A058277, A006511.
%Y A002181 Sequence in context: A024372 A061390 A051445 this_sequence A073692 A132012 
               A160690
%Y A002181 Adjacent sequences: A002178 A002179 A002180 this_sequence A002182 A002183 
               A002184
%K A002181 nonn
%O A002181 1,2
%A A002181 N. J. A. Sloane (njas(AT)research.att.com).
%E A002181 Offset and initial term corrected Oct 07 2007
%E A002181 Revised definition from T. D. Noe, Aug 14 2008

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