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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
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 (list; graph; refs; listen; history; text; internal format)
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 A141066 A018196

Adjacent sequences:  A131192 A131193 A131194 * A131196 A131197 A131198

KEYWORD

easy,nonn

AUTHOR

Alonso del Arte, Oct 20 2007

STATUS

approved

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Last modified May 19 06:41 EDT 2019. Contains 323386 sequences. (Running on oeis4.)