cp's OEIS Frontend

A254572 Least multiple of n that is abundant or perfect (A023196).

%I A254572 #24 Feb 09 2023 04:42:41
%S A254572 6,6,6,12,20,6,28,24,18,20,66,12,78,28,30,48,102,18,114,20,42,66,138,
%T A254572 24,100,78,54,28,174,30,186,96,66,102,70,36,222,114,78,40,246,42,258,
%U A254572 88,90,138,282,48,196,100,102,104,318,54,220,56,114,174,354,60
%N A254572 Least multiple of n that is abundant or perfect (A023196).
%C A254572 See A254571(n) = a(n)/n for the multipliers.
%C A254572 Very often a(n) = A064162(n), but the definition of the latter requires strict abundance.
%H A254572 Robert Israel, <a href="/A254572/b254572.txt">Table of n, a(n) for n = 1..10000</a>
%p A254572 f:= proc(n) local k; uses numtheory;
%p A254572       for k from 1 to 4 do if sigma(k*n)>=2*k*n then return k*n fi od:
%p A254572       6*n
%p A254572 end proc:
%p A254572 map(f, [$1..100]); # _Robert Israel_, Feb 10 2019
%t A254572 a[n_] := Do[If[DivisorSigma[1, k*n] >= 2*k*n, Return[k*n]], {k, {1, 2, 3, 4, 6}}];
%t A254572 Table[a[n], {n, 1, 100}] (* _Jean-François Alcover_, Feb 09 2023 *)
%o A254572 (PARI) a(n) = forstep(m=n,6*n,n,if(sigma(m)>=2*m,return(m)))
%Y A254572 Cf. A023196, A064162, A254571.
%K A254572 nonn
%O A254572 1,1
%A A254572 _Jeppe Stig Nielsen_, Feb 01 2015