cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A064606 Numbers k such that A064603(k) is divisible by k.

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%I A064606 #19 Jan 18 2024 02:42:15
%S A064606 1,2,7,45,184,210,267,732,1282,3487,98374,137620,159597,645174,
%T A064606 3949726,7867343,13215333,14153570,14262845,317186286,337222295,
%U A064606 2788845412,10937683400,72836157215,95250594634
%N A064606 Numbers k such that A064603(k) is divisible by k.
%C A064606 Analogous sequences for various arithmetical functions are A050226, A056650, A064605-A064607, A064610, A064611, A048290, A062982, A045345.
%C A064606 a(22) > 2*10^9. - _Donovan Johnson_, Jun 21 2010
%C A064606 a(26) > 10^11, if it exists. - _Amiram Eldar_, Jan 18 2024
%F A064606 (Sum_{j=1..k} sigma_3(j)) mod k = A064603(k) mod k = 0.
%e A064606 Adding divisor-cube sums for j = 1..7 gives 1+9+28+73+126+252+344 = 833 = 7*119, which is divisible by 7, so 7 is a term and the integer quotient is 119.
%t A064606 A064603 = Accumulate[Table[DivisorSigma[3, k], {k, 1, 1000000}]]; Select[Range[Length[A064603]], Divisible[A064603[[#]], #] &] (* _Vaclav Kotesovec_, Jul 11 2021 *)
%Y A064606 Cf. A001158, A064603, A050226, A056650, A064605, A064607, A064610-A064612, A048290, A062982, A045345.
%K A064606 nonn,more
%O A064606 1,2
%A A064606 _Labos Elemer_, Sep 24 2001
%E A064606 a(15)-a(21) from _Donovan Johnson_, Jun 21 2010
%E A064606 a(22)-a(25) from _Amiram Eldar_, Jan 18 2024