A348628 - OEIS

%I #4 Oct 26 2021 07:46:36

%S 1,2,3,4,15,44,674,478899

%N Numbers k such that k and k+1 have the same sum of nonexponential divisors (A160135).

%C Numbers k such that A160135(k) = A160135(k+1).

%C a(9) > 1.6 * 10^11, if it exists.

%e 2 is a term since A160135(2) = A160135(3) = 1.

%e 15 is a term since A160135(15) = A160135(16) = 9.

%t esigma[n_] := Times @@ (Sum[First[#]^d, {d, Divisors[Last[#]]}] &) /@ FactorInteger[n]; s[1] = 1; s[n_] := DivisorSigma[1, n] - esigma[n]; Select[Range[500000], s[#] == s[# + 1] &]

%Y Cf. A160135.

%Y Similar sequences: A002961, A064115, A064125, A293183, A306985, A348346.

%K nonn,more

%O 1,2

%A _Amiram Eldar_, Oct 26 2021