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 A272715 Numbers equal to the sum of their proper divisors d such that d mod 3 = 2. 2

%I

%S 280,34960,4960000,15887872,20527600,105056320,44781248512

%N Numbers equal to the sum of their proper divisors d such that d mod 3 = 2.

%C The numbers equal to the sum of their proper divisors which are a multiple of 3 are the perfect numbers (A000396) multiplied by 3.

%e The proper divisors of 280 which are congruent to 2 mod 3 are 2, 5, 8, 14, 20, 35, 56, and 140. Since their sum is 280, 280 is a term.

%t Select[Range[40000], # == Plus @@ Select[ Most@ Divisors[#], Mod[#, 3] == 2 &] &]

%o (PARI) is(n)=sumdiv(n, d, if(d%3==2, d, 0))==if(n%3==2, 2*n, n) \\ _Charles R Greathouse IV_, May 09 2016

%Y Cf. A272716, A000396, A078182 (sum of proper and improver divisors).

%K nonn,more

%O 1,1

%A _Giovanni Resta_, May 05 2016

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Last modified February 24 11:36 EST 2020. Contains 332209 sequences. (Running on oeis4.)