This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A248795 Numbers n such that Product_{d|n} phi(d) = Product_{d|(n+1)} phi(d) where phi(x) = Euler totient function (A000010). 4
 1, 3, 5, 15, 255, 65535, 2200694, 2619705, 6372794, 40588485, 76466985, 81591194, 118018094, 206569605, 470542485, 525644385, 726638834, 791937614, 971122514, 991172805 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that A029940(n) = A029940(n+1). 4294967295 is in this sequence. LINKS 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: A270548 A292339 A175138 * A215444 A006593 A115724 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 15 11:03 EDT 2018. Contains 316224 sequences. (Running on oeis4.)