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A055197 Numbers k such that A005728(k) is not prime. 4


%S 10,14,16,19,20,21,25,26,27,28,30,31,32,33,34,35,38,39,41,42,43,44,45,

%T 46,47,48,49,50,51,52,54,56,57,58,64,65,66,67,70,71,72,73,75,76,77,78,

%U 79,80,81,82,84,85,87,88,89,90,91,92,94,95,96,98,99,100

%N Numbers k such that A005728(k) is not prime.

%C From a question posed by Leo Moser.

%D Martin Gardner, "The Last Recreations," Chapter entitled "Strong Laws of Small Primes," Copernicus, Springer-Verlag, NY, 1997, page 199.

%H Amiram Eldar, <a href="/A055197/b055197.txt">Table of n, a(n) for n = 1..10000</a>

%H Leo Moser, <a href="https://books.google.com/books?id=u6N0yfe69RcC&amp;pg=PA312">Problem P42</a>, Canadian Mathematical Bulletin, Vol. 5, No. 3 (1962), pp. 312-313.

%t s=1; Do[ s=s+EulerPhi[ n ]; If[ !PrimeQ[ s ], Print[ n ] ], {n, 1, 100} ]

%Y Cf. A005728.

%Y Complement of A055201.

%K easy,nonn

%O 1,1

%A _Robert G. Wilson v_, Jul 04 2000

%E Offset corrected by _Amiram Eldar_, Mar 01 2020

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Last modified April 9 03:15 EDT 2020. Contains 333343 sequences. (Running on oeis4.)