OFFSET
1,2
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..213 (terms below 10^13, calculated using the b-file at A001274)
EXAMPLE
15 is in the sequence because phi(15) = phi(16) = 8 and simultaneously Product_{d|15} phi(d) = Product_{d|(15+1)} phi(d) = 64.
MATHEMATICA
a247174[n_Integer] := Module[{a001274, a248795},
a001274[m_] := Select[Range[m], EulerPhi[#] == EulerPhi[# + 1] &];
a248795[m_] :=
Select[Range[m],
Product[EulerPhi[i], {i, Divisors[#]}] ==
Product[EulerPhi[j], {j, Divisors[# + 1]}] &];
Intersection[a001274[n], a248795[n]]] (* Michael De Vlieger, Dec 01 2014 *)
PROG
(Magma) [n: n in [1..100000] | (&*[EulerPhi(d): d in Divisors(n)]) eq (&*[EulerPhi(d): d in Divisors(n+1)]) and EulerPhi(n) eq EulerPhi(n+1)]
(Magma) [n: n in [A248795(n)] | EulerPhi(n) eq EulerPhi(n+1)]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Nov 22 2014
EXTENSIONS
a(6)-a(19) using A248795 by Jaroslav Krizek, Nov 25 2014
STATUS
approved