

A028476


Greatest k such that phi(k) = phi(n), where phi is Euler's totient function.


7



2, 2, 6, 6, 12, 6, 18, 12, 18, 12, 22, 12, 42, 18, 30, 30, 60, 18, 54, 30, 42, 22, 46, 30, 66, 42, 54, 42, 58, 30, 62, 60, 66, 60, 90, 42, 126, 54, 90, 60, 150, 42, 98, 66, 90, 46, 94, 60, 98, 66, 120, 90, 106, 54, 150, 90, 126, 58, 118, 60, 198, 62, 126, 120, 210, 66, 134
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OFFSET

1,1


COMMENTS

Every number in this sequence occurs at least twice. For all n > 6, a(n) > phi(n)^2 is impossible.  Alonso del Arte, Dec 31 2016


LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000 (computed from the bfile of A057826 provided by T. D. Noe)


FORMULA

a(1) = a(2) = 2, for n > 2, a(n) = A057826(A000010(n)/2).  Antti Karttunen, Aug 07 2017


EXAMPLE

phi(1) = 1 and phi(2) = 1 also. There is no greater k such that phi(k) = 1, so therefore a(1) = a(2) = 2.
phi(3) = phi(4) = phi(6) = 2, and there is no greater k such that phi(k) = 6, hence a(3) = a(4) = a(6) = 6.


MATHEMATICA

Table[Module[{k = (2 Boole[n <= 6]) + #^2}, While[EulerPhi@ k != #, k]; k] &@ EulerPhi@ n, {n, 120}] (* Michael De Vlieger, Dec 31 2016 *)


CROSSREFS

Cf. A000010, A015126, A057826, A066412, A066659, A071181.
Sequence in context: A032043 A200561 A241380 * A179478 A051548 A110660
Adjacent sequences: A028473 A028474 A028475 * A028477 A028478 A028479


KEYWORD

nonn


AUTHOR

Vladeta Jovovic, Jan 12 2002


STATUS

approved



