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

Author

Robert G. Wilson v, Jul 04 2000

Keywords

• easy
• nonn

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.

Crossrefs

Cf. A005728.

Complement of A055201.

Programs

Mathematica

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

Extensions

Offset corrected by Amiram Eldar, Mar 01 2020