A379917 a(n) is the deficiency of A046390(n), divided by 2.

3, 21, 57, 75, 129, 111, 213, 315, 165, 255, 183, 291, 345, 339, 237, 471, 273, 549, 453, 291, 609, 465, 525, 327, 973, 507, 707, 705, 381, 615, 681, 669, 633, 435, 903, 453, 1361, 795, 939, 717, 1023, 507, 759, 1017, 831, 1245, 1555, 915, 543, 561, 1687, 843, 993

Offset: 1

Author

Hugo Pfoertner, Jan 06 2025

Keywords

• nonn
• look

Links

• Hugo Pfoertner, Table of n, a(n) for n = 1..10000
• Michael De Vlieger, Log log scatterplot of a(n), n = 1..177395.

Crossrefs

Cf. A000203, A033879, A046390, A378717, A379915, A379916.

Programs

Mathematica

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 *)

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,", ")));
a379915_17(8000,4)

Formula

a(n) = (2*A046390(n) - sigma(A046390(n)))/2, where sigma is A000203.

a(n) = A033879(A046390(n))/2.