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

1,2

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

Links

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

Example

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).

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]

Crossrefs

Cf. A000010, A000040, A006005.

Sequence in context: A023886 A158337 A161542 * A020217 A370999 A329728

Adjacent sequences: A131192 A131193 A131194 * A131196 A131197 A131198

Keyword

easy,nonn

Author

Alonso del Arte, Oct 20 2007

Status

approved