login
A222711
Numbers k such that gcd(sigma(k), phi(k)) (A009223) attains record values.
2
1, 3, 12, 14, 15, 35, 105, 190, 248, 357, 616, 812, 1045, 3080, 3135, 3339, 4064, 5049, 8323, 8636, 10659, 12441, 16065, 19780, 20026, 23374, 24871, 29029, 50065, 58435, 64285, 87685, 124355, 132957, 137885, 140335, 248501, 263055, 317205, 353133, 423657, 596037, 655707, 734517, 894387
OFFSET
1,2
COMMENTS
RECORDS transform of A009223.
LINKS
N. J. A. Sloane, Transforms (The RECORDS transform returns both the high-water marks and the places where they occur).
MATHEMATICA
a[1] = 1; record = 1; a[n_] := a[n] = For[k = a[n-1] + 1, True, k++, g = GCD[DivisorSigma[1, k], EulerPhi[k]]; If[g > record, record = g; Return[k]]]; Table[a[n], {n, 1, 45}] (* Jean-François Alcover, Oct 07 2013 *)
DeleteDuplicates[Table[{k, GCD[DivisorSigma[1, k], EulerPhi[k]]}, {k, 900000}], GreaterEqual[ #1[[2]], #2[[2]]]&][[;; , 1]] (* Harvey P. Dale, Jun 22 2024 *)
PROG
(PARI) mg=0; for(x=1, 1000000, g=A009223(x); if(g>mg, print1(x", "); mg=g))
CROSSREFS
Sequence in context: A117061 A341799 A089919 * A176796 A242130 A286386
KEYWORD
nonn,nice
AUTHOR
Phil Carmody, Mar 01 2013
STATUS
approved