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

1,1

Links

Table of n, a(n) for n=1..37.

Example

10680 is in this sequence because sigma(10680)=180^2 and sigma(10681)=108^2. - Sean A. Irvine, Sep 04 2023

Mathematica

nn = 300000; SequencePosition[Array[GCD @@ FactorInteger[DivisorSigma[1, #]][[All, -1]] &, nn + 1], {_?(# > 1 &), _?(# > 1 &)}][[All, 1]] (* Michael De Vlieger, Sep 04 2023 *)

Crossrefs

Cf. A065496.

Sequence in context: A119109 A254603 A144856 * A218844 A219423 A123213

Adjacent sequences: A065519 A065520 A065521 * A065523 A065524 A065525

Keyword

nonn

Author

Robert G. Wilson v, Nov 27 2001

Extensions

Missing terms inserted by Sean A. Irvine, Sep 04 2023

Status

approved