A131195 Nonprime record values of Euler's totient function (A000010): 1 and composite n such that phi(n) is greater than all smaller composites.

1, 4, 8, 9, 15, 21, 25, 35, 49, 65, 77, 85, 91, 115, 119, 121, 143, 161, 169, 187, 203, 209, 221, 247, 253, 287, 289, 319, 323, 341, 361, 391, 403, 437, 451, 473, 481, 493, 517, 527, 529, 583, 589, 611, 629, 649, 667, 689, 697, 703, 713, 731, 767, 779, 799, 817

Offset: 1

Author

Alonso del Arte, Oct 20 2007

Keywords

• easy
• nonn

Comments

Since phi(p) = p - 1, allowing prime numbers in this sequence would make it A006005, the primes with a 1 replacing the initial 2.

Number of terms < 10^k, k=1,2,3,...: 4, 13, 61, 310, 1628, 9029, 51207, 295132, ..., . Robert G. Wilson v, Feb 19 2019

Examples

			a(3) = 8 because phi(8) = 4, which is greater than phi(4) = phi(6) = 2. (phi(5) = 4 and phi(7) = 6 are ignored because 5 and 7 are prime).
		

Links

• Robert G. Wilson v, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A000040, A006005.

Programs

Mathematica

htcList = {1}; i = 4; currMax = 1; searchMax = 1000; While[i < searchMax, If[Not[PrimeQ[i]] && EulerPhi[i] > currMax, htcList = {htcList, i}; currMax = EulerPhi[i]]; i++ ]; Flatten[htcList]