A065393 Sigma(phi(m)) - phi(sigma(m)) is increasing at these values of m.

3, 5, 7, 11, 13, 17, 19, 29, 31, 37, 41, 53, 61, 73, 95, 97, 109, 127, 143, 157, 181, 209, 241, 287, 313, 323, 337, 377, 403, 407, 421, 473, 527, 533, 541, 589, 601, 661, 713, 731, 757, 779, 899, 1009, 1073, 1147, 1159, 1199, 1271, 1321, 1333, 1349, 1517

Offset

1,1

Comments

First composite number is the 15th term, 95. [Corrected by Jacob Vecht, Jul 28 2020]

Links

Harry J. Smith, Table of n, a(n) for n = 1..500

Mathematica

a = 0; s = 0; Do[s = DivisorSigma[1, EulerPhi[n]] - EulerPhi[DivisorSigma[1, n]]; If[s>a, a = s; Print[n]], {n, 1, 10000}]
DeleteDuplicates[Table[{m, DivisorSigma[1, EulerPhi[m]]-EulerPhi[DivisorSigma[1, m]]}, {m, 1600}], GreaterEqual[#1[[2]], #2[[2]]]&][[;; , 1]] (* Harvey P. Dale, Aug 02 2023 *)

Prog

(PARI) { n=r=0; for (m=1, 10^9, x=sigma(eulerphi(m)) - eulerphi(sigma(m)); if (x > r, r=x; write("b065393.txt", n++, " ", m); if (n==500, return)) ) } \\ Harry J. Smith, Oct 18 2009

Crossrefs

Cf. A000010, A000203, A065394, A065395.

Sequence in context: A325143 A276357 A065041 * A179740 A186884 A045393

Adjacent sequences: A065390 A065391 A065392 * A065394 A065395 A065396

Keyword

nonn

Author

Labos Elemer, Nov 05 2001

Status

approved