A074390 - OEIS

A074390

a(n) is the least number that A074389(a[n])=n.

1, 6, 18, 12, 200, 42, 196, 56, 459, 950, 5203, 396, 9243, 980, 1800, 336, 19363, 270, 13357, 600, 1764, 10406, 72473, 168, 18625, 34814, 4293, 812, 145493, 1350, 15376, 992, 19602, 38726, 41615, 1836, 99937, 26714, 1521, 440, 274003, 3822, 475193

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..43.

FORMULA

a(n)=Min{x; GCD[x, sigma(x), Phi(x)]}= Min{x; GCD[A000005(x), A000010(x), x]}=n

EXAMPLE

n=79: a(79)=979837 because GCD[979837,998718,961272]=79 and a(79) is the smallest.

MATHEMATICA

f[x_] := GCD[DivisorSigma[1, x], EulerPhi[x], x] t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 1000000}];

CROSSREFS

Cf. A000005, A000010, A073815, A050399, A009195, A009194.

Sequence in context: A097370 A252897 A174904 * A255617 A253771 A223218

Adjacent sequences: A074387 A074388 A074389 * A074391 A074392 A074393

KEYWORD

nonn

AUTHOR

Labos Elemer, Aug 23 2002

STATUS

approved