A348585 Numbers k such that A113184(k) = A113184(k+1).

1, 8, 27, 375, 459, 620, 1652, 2871, 3451, 3956, 8055, 8636, 8907, 9844, 10647, 12104, 19491, 20155, 27089, 27643, 38180, 41547, 48364, 62379, 74875, 79304, 83780, 90692, 115289, 139460, 146828, 233729, 291819, 297987, 324423, 338547, 365660, 377540, 392635, 403575

Offset

1,2

Comments

Equivalently, numbers k such that A002129(k) = -A002129(k+1).

Links

Amiram Eldar, Table of n, a(n) for n = 1..250

Example

1 is a term since A113184(1) = A113184(2) = 1.
8 is a term since A113184(8) = A113184(9) = 13.

Mathematica

f[p_, e_] := If[p == 2, 2^(e + 1)-3, (p^(e + 1) - 1)/(p - 1)]; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[10^5], s[#] == s[# + 1] &]

Prog

(PARI) f(n) = -sumdiv(n, d, (-1)^d*d); \\ A002129
isok(k) = f(k) + f(k+1) == 0; \\ Michel Marcus, Oct 24 2021

Crossrefs

Cf. A002129, A113184.

Similar sequences: A002961, A206368, A333261.

Sequence in context: A115694 A028935 A030089 * A007235 A029789 A155930

Adjacent sequences: A348582 A348583 A348584 * A348586 A348587 A348588

Keyword

nonn

Author

Amiram Eldar, Oct 24 2021

Status

approved