|
%I #23 Jul 24 2018 09:46:32
%S 1,4,13,32,104,228,576,1408,4104,9824,19152,39816,82944,196992,441294,
%T 881280,1911168,4539024
%N a(n) is the sum of the divisors of the smallest number k such that the symmetric representation of sigma(k) has n parts.
%C For more information see A239663 and A239665.
%F a(n) = A000203(A239663(n)).
%e Illustration of the symmetric representation of sigma(9):
%e .
%e . _ _ _ _ _ 5
%e . |_ _ _ _ _|
%e . |_ _ 3
%e . |_ |
%e . |_|_ _ 5
%e . | |
%e . | |
%e . | |
%e . | |
%e . |_|
%e .
%e For n = 3 we have that 9 is the smallest number whose symmetric representation of sigma has three parts: [5, 3, 5], so a(3) = 5 + 3 + 5 = 13, equaling the sum of divisors of 9: sigma(9) = 1 + 3 + 9 = 13.
%e For n = 7 we have that 357 is the smallest number whose symmetric representation of sigma has seven parts: [179, 61, 29, 38, 29, 61, 179], so a(7) = 179 + 61 + 29 + 38 + 29 + 61 + 179 = 576, equaling the sum of divisors of 357: sigma(357) = 1 + 3 + 7 + 17 + 21 + 51 + 119 + 357 = 576.
%Y Cf. A000203, A196020, A235791, A236104, A237048, A237270, A237271, A237591, A237593, A239931-A239934, A239663, A239665, A240062, A245092, A262626.
%K nonn,hard,more
%O 1,2
%A _Omar E. Pol_, Dec 21 2015
%E a(14)-a(18) from _Omar E. Pol_, Jul 21 2018
|
