Search: id:A001838
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%I A001838 M2397
%S A001838 3,5,6,11,12,14,17,18,20,29,41,44,59,62,71,92,101,107,116,137,149,164,
%T A001838 179,191,197,212,227,239,254,269,281,311,332,347,356,419,431,452,461,
%U A001838 521,524,569,599,617,641,659,692,716,764,809,821,827,857,881,932,956
%N A001838 Numbers n such that phi(n+2) = phi(n) + 2.
%C A001838 If p and p+2 are primes then p is a solution. If p and 2p+1 are both 
               odd primes then 4p is a solution. Several numbers of the form 2^i-2 
               are solutions (see cross referenced sequences). Although 18 is a 
               solution, it is not of any of these forms.
%C A001838 Twice Mersenne primes (cf. A000668) are also solutions. - Vladeta Jovovic 
               (vladeta(AT)eunet.rs), Feb 14 2002
%D A001838 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A001838 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.
%D A001838 L. Moser, Some equations involving Euler's totient function, Amer. Math. 
               Monthly, 56 (1949), 22-23.
%D A001838 D. M. Burton, Elementry Number Theory, section 7-2.
%H A001838 T. D. Noe, <a href="b001838.txt">Table of n, a(n) for n=1..10000</a>
%H A001838 M. Abramowitz and I. A. Stegun, eds., <a href="http://www.nrbook.com/
               abramowitz_and_stegun/">Handbook of Mathematical Functions</a>, National 
               Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 
               [alternative scanned copy].
%e A001838 phi(18)+2=8=phi(18+2), so 18 is in the sequence.
%Y A001838 Cf. A050472, A050473, etc. Essentially the same as A056853.
%Y A001838 Sequence in context: A115059 A092835 A167522 this_sequence A080759 A145714 
               A047443
%Y A001838 Adjacent sequences: A001835 A001836 A001837 this_sequence A001839 A001840 
               A001841
%K A001838 nonn,nice
%O A001838 1,1
%A A001838 N. J. A. Sloane (njas(AT)research.att.com).
%E A001838 More terms from Jud McCranie (j.mccranie(AT)comcast.net), Dec 24 1999

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