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A050399 Least k such that n = A009195(k) (= gcd(phi(k), k)). 8
1, 4, 9, 8, 25, 18, 49, 16, 27, 50, 121, 36, 169, 98, 225, 32, 289, 54, 361, 100, 147, 242, 529, 72, 125, 338, 81, 196, 841, 450, 961, 64, 1089, 578, 1225, 108, 1369, 722, 507, 200, 1681, 294, 1849, 484, 675, 1058, 2209, 144, 343, 250, 2601, 676, 2809 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Coincides with A072995 for many terms, but differs, e.g., in n = 20, 40, 52, ... in addition to the zeros in A072995. See also the comments in A072994. - M. F. Hasler, Feb 23 2014

a(n) <= n^2. - Robert G. Wilson v, Feb 27 2014

LINKS

Robert G. Wilson v, Table of n, a(n) for n = 1..10000

MATHEMATICA

t = Table[0, {10000}]; k = 1; While[k < 100000001, a = GCD[k, EulerPhi@ k]; If[a < 10001 && t[[a]] == 0, t[[a]] = k; Print[{a, k}]]; k++]; t (* Robert G. Wilson v, Feb 27 2014 *)

PROG

(PARI) A050399=n->for(k=1, 9e9, gcd(eulerphi(k), k)==n&&return(k)) \\ M. F. Hasler, Feb 23 2014

CROSSREFS

Sequence in context: A280286 A268597 A253560 * A072995 A073395 A064549

Adjacent sequences:  A050396 A050397 A050398 * A050400 A050401 A050402

KEYWORD

nonn

AUTHOR

Christian G. Bower, Nov 15 1999

STATUS

approved

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Last modified June 14 21:27 EDT 2021. Contains 345041 sequences. (Running on oeis4.)