OFFSET
1,4
COMMENTS
a(n) <= A210500(n).
REFERENCES
Alexander S. Karpenko, Lukasiewicz's Logics and Prime Numbers, Luniver Press, Beckington, 2006, pp. 52-56.
LINKS
Arkadiusz Wesolowski, Table of n, a(n) for n = 1..1000
EXAMPLE
The set {k: phi(k) = 12} is {13, 21, 26, 28, 36, 42}. Thus, if phi(k) = prime(6) - 1, the equation has exactly two odd solutions. Hence, a(6) = 2.
MATHEMATICA
r = 87; lst1 = Table[EulerPhi[n], {n, (Prime[r] - 1)^2 + 1}]; lst2 = {}; Do[p = Prime[n]; AppendTo[lst2, Length@Select[Flatten@Position[Take[lst1, {p - 1, (p - 1)^2 + 1}], Prime[n] - 1], EvenQ]], {n, r}]; lst2
CROSSREFS
KEYWORD
nonn
AUTHOR
Arkadiusz Wesolowski, Jan 19 2013
STATUS
approved