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

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

Amiram Eldar, Table of n, a(n) for n = 1..10000

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

Adjacent sequences: A055194 A055195 A055196 * A055198 A055199 A055200

Keyword

easy,nonn

Author

Robert G. Wilson v, Jul 04 2000

Extensions

Offset corrected by Amiram Eldar, Mar 01 2020

Status

approved