cp's OEIS Frontend

A357921 Primitive abundant numbers for which there is no smaller primitive abundant number having the same ordered prime signature.

%I A357921 #10 Oct 23 2022 23:45:23
%S A357921 20,70,88,272,550,572,945,1184,1430,1575,2205,3465,4288,5775,7425,
%T A357921 8085,12705,15015,16768,24272,28215,47025,49875,65792,69825,78975,
%U A357921 81081,103455,131625,152224,153153,182325,189189,266752,297297,342225,351351,363375,387345,392445,474045
%N A357921 Primitive abundant numbers for which there is no smaller primitive abundant number having the same ordered prime signature.
%e A357921 550 is in the sequence as it is primitive abundant and it is the smallest primitive abundant number having its prime signature (in this case (1,2,1)). No positive integer < 550 is a primitive abundant and has prime signature (1,2,1).
%o A357921 (PARI) upto(n) = { m = Map(); res = List(); forfactored(i = 1, n, if(!mapisdefined(m, i[2][,2]), if(isA071395(i[1]), mapput(m, i[2][,2], i[1]); listput(res, i[1]) ) ) ); res }
%o A357921 isA071395(v) = {if (sigma(v) <= 2*v, return (0)); fordiv (v, d, if ((d != v) && (sigma(d) >= 2*d), return (0)); ); return (1); } \\ isA071395 from _Michel Marcus_ at A071395
%Y A357921 Supersequence of A083873.
%Y A357921 Cf. A025487, A071395.
%K A357921 nonn
%O A357921 1,1
%A A357921 _David A. Corneth_, Oct 20 2022