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A340720 Least positive number k such that sigma(k) = n * sigma(k+1). 2

%I

%S 14,12,180,25908120

%N Least positive number k such that sigma(k) = n * sigma(k+1).

%e n | sigma(a(n)) | sigma(a(n)+1)

%e ----+-------------+--------------

%e 1 | 24 | 24

%e 2 | 28 | 14

%e 3 | 546 | 182

%e 4 | 103680000 | 25920000

%o (PARI) {a(n) = my(k=1); while(sigma(k)!=n*sigma(k+1), k++); k}

%Y Cf. A002961, A080372, A163193, A217791, A340715.

%K nonn,more,hard

%O 1,1

%A _Seiichi Manyama_, Jan 17 2021

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Last modified August 10 06:08 EDT 2022. Contains 356029 sequences. (Running on oeis4.)