A065522 Numbers k such that sigma(k) and sigma(k+1) are nontrivial powers (A065496).
21, 93, 381, 1065, 1173, 5065, 5670, 5729, 6603, 8809, 10281, 10680, 15960, 17110, 39286, 40526, 47882, 49951, 61962, 85058, 85261, 99066, 117860, 125985, 126853, 135890, 143241, 159901, 171945, 179556, 185853, 208744, 209585, 210450, 251394, 261767, 288792
Offset: 1
Keywords
Examples
10680 is in this sequence because sigma(10680)=180^2 and sigma(10681)=108^2. - _Sean A. Irvine_, Sep 04 2023
Crossrefs
Cf. A065496.
Programs
-
Mathematica
nn = 300000; SequencePosition[Array[GCD @@ FactorInteger[DivisorSigma[1, #]][[All, -1]] &, nn + 1], {?(# > 1 &), ?(# > 1 &)}][[All, 1]] (* Michael De Vlieger, Sep 04 2023 *)
Extensions
Missing terms inserted by Sean A. Irvine, Sep 04 2023