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A055197 A005728(n) is not prime. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

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

Table of n, a(n) for n=0..63.

MATHEMATICA

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

CROSSREFS

Cf. A005728.

Sequence in context: A067188 A092632 A213310 * A116610 A289698 A153041

Adjacent sequences:  A055194 A055195 A055196 * A055198 A055199 A055200

KEYWORD

easy,nonn

AUTHOR

Robert G. Wilson v, Jul 04 2000

STATUS

approved

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Last modified February 17 23:35 EST 2020. Contains 332006 sequences. (Running on oeis4.)