A248796 - OEIS

A248796

Numbers n such that Product_{d|(n-2)} phi(d) = Product_{d|(n-1)} phi(d) where phi(x) = Euler totient function (A000010).

3, 5, 7, 17, 257, 65537, 2200696, 2619707, 6372796, 40588487, 76466987, 81591196, 118018096, 206569607, 470542487, 525644387, 726638836, 791937616, 971122516, 991172807

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OFFSET

1,1

COMMENTS

Numbers n such that A029940(n-2) = A029940(n-1).

The first 5 known Fermat primes (A019434) are terms of this sequence.

Supersequence of A247164 and A247203.

LINKS

Table of n, a(n) for n=1..20.

FORMULA

a(n) = A248795(n)+2.

A029940(a(n)) = a(n)-1 if a(n) = prime.

EXAMPLE

17 is in the sequence because A029940(15) = A029940(16) = 64.

PROG

(Magma) [n: n in [3..100000] | (&*[EulerPhi(d): d in Divisors(n-2)]) eq (&*[EulerPhi(d): d in Divisors(n-1)])]

CROSSREFS

Cf. A000010, A019434, A029940, A247164, A248795.

Sequence in context: A229132 A270779 A350176 * A247164 A064080 A184875

Adjacent sequences: A248793 A248794 A248795 * A248797 A248798 A248799

KEYWORD

nonn,more

AUTHOR

Jaroslav Krizek, Nov 19 2014

EXTENSIONS

a(7)-a(9) using A248795 by Jaroslav Krizek, Nov 19 2014

a(10)-a(20) using A248795 by Jaroslav Krizek, Nov 25 2014

STATUS

approved