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

1,1

Links

Hugo Pfoertner, Table of n, a(n) for n = 1..10000

Michael De Vlieger, Log log scatterplot of a(n), n = 1..177395.

Formula

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

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

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 *)

Prog

(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)

Crossrefs

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

Sequence in context: A181156 A356809 A162394 * A129212 A354850 A328042

Adjacent sequences: A379914 A379915 A379916 * A379919 A379920 A379921

Keyword

nonn,look,new

Author

Hugo Pfoertner, Jan 06 2025

Status

approved