A353901 - OEIS

%I #5 May 10 2022 14:27:03

%S 1,6,28,56,1104,2208,2178540,4357080,6499584,12999168

%N Numbers k such that A353900(k) is divisible by k.

%C a(11) > 8*10^10, if it exists.

%C The corresponding ratios A353900(k)/k are 1, 2, 2, 1, 2, 1, 4, 2, 2, 1, ...

%e 6 is a term since A353900(6) = 12 is divisible by 6.

%e 56 is a term since A353900(56) = 56 is divisible by 56.

%t f[p_, e_] := 1 + Sum[p^(2^k), {k, 0, Floor[Log2[e]]}]; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[6.5*10^6], Divisible[s[#], #] &]

%Y Cf. A353900.

%Y Similar sequences: A007691, A189000, A327158, A348601.

%K nonn,more

%O 1,2

%A _Amiram Eldar_, May 10 2022