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A055197
Numbers k such that A005728(k) is not prime.
4
10, 14, 16, 19, 20, 21, 25, 26, 27, 28, 30, 31, 32, 33, 34, 35, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 54, 56, 57, 58, 64, 65, 66, 67, 70, 71, 72, 73, 75, 76, 77, 78, 79, 80, 81, 82, 84, 85, 87, 88, 89, 90, 91, 92, 94, 95, 96, 98, 99, 100
OFFSET
1,1
COMMENTS
From a question posed by Leo Moser.
REFERENCES
Martin Gardner, "The Last Recreations," Chapter entitled "Strong Laws of Small Primes," Copernicus, Springer-Verlag, NY, 1997, page 199.
LINKS
Leo Moser, Problem P42, Canadian Mathematical Bulletin, Vol. 5, No. 3 (1962), pp. 312-313.
MATHEMATICA
s=1; Do[ s=s+EulerPhi[ n ]; If[ !PrimeQ[ s ], Print[ n ] ], {n, 1, 100} ]
CROSSREFS
Cf. A005728.
Complement of A055201.
Sequence in context: A067188 A092632 A213310 * A116610 A289698 A153041
KEYWORD
easy,nonn
AUTHOR
Robert G. Wilson v, Jul 04 2000
EXTENSIONS
Offset corrected by Amiram Eldar, Mar 01 2020
STATUS
approved