A128859 Let p be the n-th odd prime; a(n) is the number of primitive roots of p which are <= (p-1)/2.

0, 1, 1, 1, 2, 4, 2, 4, 6, 4, 6, 8, 6, 9, 12, 10, 8, 10, 9, 12, 10, 16, 20, 16, 20, 13, 22, 18, 24, 17, 18, 32, 18, 36, 16, 24, 26, 36, 42, 37, 24, 29, 32, 42, 23, 16, 38, 49, 36, 56, 44, 32, 44, 64, 59, 66, 33, 44, 48, 40, 72, 48, 55, 48, 78, 35, 48, 79, 56, 80, 80, 60, 60, 55

Offset: 1

Author

N. J. A. Sloane, Apr 20 2007

Keywords

• nonn
• easy

References

• Roger Osborn, Tables of All Primitive Roots of Odd Primes Less Than 1000, Univ. Texas Press, Austin, TX, 1961, pp. 69-70.

Links

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

Crossrefs

Cf. A118818.

Programs

Mathematica

a[n_] := Count[PrimitiveRootList[(p = Prime[n+1])], _?(# <= (p-1)/2 &)]; Array[a, 100]

Extensions

More terms from Don Reble, Apr 20 2007