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A081397 a(n) = least k such that GCD of sigma(k) = A000203(k) and phi(k) = A000010(k) equals n-th primorial = A002110(n). 1
3, 14, 488, 16072, 284229, 29221621, 25014312576 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(8) <= 1524139588224. - Donovan Johnson, Dec 14 2009

LINKS

Table of n, a(n) for n=1..7.

FORMULA

a(n) = Min_{k : A081396(k) = A002110(n)}.

EXAMPLE

k=284229: sigma(284229) = 482790 = 2*3*5*7*11*19, phi(284229) = 166320 = 2*2*2*3*3*3*3*5*7*11, common factor set = {2,3,5,7,11}, gcd(sigma,phi) = 2310.

CROSSREFS

Cf. A000010, A000203, A002110, A081383, A081396.

Sequence in context: A297487 A297484 A289878 * A264748 A092987 A088334

Adjacent sequences: A081394 A081395 A081396 * A081398 A081399 A081400

KEYWORD

nonn,more

AUTHOR

Labos Elemer, Mar 28 2003

EXTENSIONS

a(6) corrected and a(7) from Donovan Johnson, Dec 14 2009

STATUS

approved

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Last modified December 5 13:26 EST 2022. Contains 358586 sequences. (Running on oeis4.)