A068401 Numbers k such that sigma(k) = phi(k+1) + phi(k-1).

2, 38, 62, 346, 1298, 7898, 22682, 24382, 93022, 108194, 143362, 171982, 192718, 264766, 587638, 986642, 1236898, 1441042, 1604422, 2228582, 4146434, 5070314, 5631718, 6687046, 10223918, 10695182, 12465158, 14221738, 15148522, 21718622, 23660038, 31290398, 31390454

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..90

Mathematica

Select[Range[2, 125*10^5], DivisorSigma[1, #]==Total[EulerPhi[#+{1, -1}]]&] (* Harvey P. Dale, Jan 22 2020 *)

Prog

(PARI) for(n=2, 12500000, if(sigma(n)==eulerphi(n+1)+eulerphi(n-1), print1(n, ", ")))

Crossrefs

Cf. A000010, A000203.

Sequence in context: A049487 A163792 A050899 * A173026 A294396 A075459

Adjacent sequences: A068398 A068399 A068400 * A068402 A068403 A068404

Keyword

nonn

Author

Benoit Cloitre, Mar 02 2002

Extensions

More terms from Rick L. Shepherd, Jul 04 2002

More terms from Amiram Eldar, Jun 14 2022

Status

approved