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%I #19 Jan 09 2025 13:19:57
%S 3,21,57,75,129,111,213,315,165,255,183,291,345,339,237,471,273,549,
%T 453,291,609,465,525,327,973,507,707,705,381,615,681,669,633,435,903,
%U 453,1361,795,939,717,1023,507,759,1017,831,1245,1555,915,543,561,1687,843,993
%N a(n) is the deficiency of A046390(n), divided by 2.
%H Hugo Pfoertner, <a href="/A379917/b379917.txt">Table of n, a(n) for n = 1..10000</a>
%H Michael De Vlieger, <a href="/A379917/a379917.png">Log log scatterplot of a(n)</a>, n = 1..177395.
%F a(n) = (2*A046390(n) - sigma(A046390(n))/2, where sigma is A000203.
%F a(n) = (A033879(A046390(n))/2.
%t Map[(2 # - DivisorSigma[1, #])/2 &, Select[Range[1, 8001, 2], PrimeNu[#] == PrimeOmega[#] == 4 &] ] (* _Michael De Vlieger_, Jan 09 2025, after _Harvey P. Dale_ at A046390 *)
%o (PARI) a379915_17(limit,np=2) = forstep(k=15, limit, 2, my(f=factor(k)); if(omega(f)==np && bigomega(f)==np, print1((2*k-sigma(f))/2,", ")));
%o a379915_17(8000,4)
%Y Cf. A000203, A033879, A046390, A378717, A379915, A379916.
%K nonn,look
%O 1,1
%A _Hugo Pfoertner_, Jan 06 2025