A248795 - OEIS

A248795

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

1, 3, 5, 15, 255, 65535, 2200694, 2619705, 6372794, 40588485, 76466985, 81591194, 118018094, 206569605, 470542485, 525644385, 726638834, 791937614, 971122514, 991172805

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OFFSET

1,2

COMMENTS

Numbers n such that A029940(n) = A029940(n+1).

4294967295 is in this sequence.

LINKS

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

FORMULA

a(n) = A248796(n)-2.

EXAMPLE

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

MATHEMATICA

a248795[n_Integer] := Select[Range[n],

Product[EulerPhi[i], {i, Divisors[#]}] ==

Product[EulerPhi[j], {j, Divisors[# + 1]}] &]; a248795[10^5] (* Michael De Vlieger, Nov 30 2014 *)

PROG

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

(PARI) lista(nn) = {d = divisors(1); vcur = prod(k=1, #d, eulerphi(d[k])); for (n=2, nn, d = divisors(n); vnext = prod(k=1, #d, eulerphi(d[k])); if (vnext == vcur, print1(n-1, ", ")); vcur = vnext; ); } \\ Michel Marcus, Nov 23 2014

CROSSREFS

Cf. A000010, A019434, A029940, A248796.

Sequence in context: A292339 A374463 A175138 * A215444 A378176 A325257

Adjacent sequences: A248792 A248793 A248794 * A248796 A248797 A248798

KEYWORD

nonn,more

AUTHOR

Jaroslav Krizek, Nov 19 2014

EXTENSIONS

a(7)-a(9) from Michel Marcus, Nov 21 2014

a(10)-a(20) from Michel Marcus, Nov 23 2014

STATUS

approved