This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A379917 #22 Mar 31 2025 22:58:21 %S A379917 3,21,57,75,129,111,213,315,165,255,183,291,345,339,237,471,273,549, %T A379917 453,291,609,465,525,327,973,507,707,705,381,615,681,669,633,435,903, %U A379917 453,1361,795,939,717,1023,507,759,1017,831,1245,1555,915,543,561,1687,843,993 %N A379917 a(n) is the deficiency of A046390(n), divided by 2. %H A379917 Hugo Pfoertner, <a href="/A379917/b379917.txt">Table of n, a(n) for n = 1..10000</a> %H A379917 Michael De Vlieger, <a href="/A379917/a379917.png">Log log scatterplot of a(n)</a>, n = 1..177395. %F A379917 a(n) = (2*A046390(n) - sigma(A046390(n)))/2, where sigma is A000203. %F A379917 a(n) = A033879(A046390(n))/2. %t A379917 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 A379917 (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 A379917 a379915_17(8000,4) %Y A379917 Cf. A000203, A033879, A046390, A378717, A379915, A379916. %K A379917 nonn,look %O A379917 1,1 %A A379917 _Hugo Pfoertner_, Jan 06 2025