A067799 Numbers k such that phi(k) + phi(k+1) = sigma(k).

2, 3, 5, 115, 143, 287, 371, 413, 623, 791, 4067, 10031, 24149, 32335, 39689, 88403, 93443, 107365, 148735, 168833, 212993, 427763, 555947, 650095, 925253, 1017821, 1117457, 1139467, 1229327, 1270801, 1407295, 2184221, 2294509, 2913757, 3258355, 4699981, 5747291

Offset: 1

Author

Benoit Cloitre, Feb 07 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..138

Crossrefs

Cf. A000010, A000203, A092404.

Programs

Mathematica

Select[Range[10^6], EulerPhi[#] + EulerPhi[# + 1] == DivisorSigma[1, #] &] (* Amiram Eldar, May 21 2022 *)

Extensions

More terms from Dean Hickerson, Feb 16 2002

More terms from Amiram Eldar, May 21 2022