OFFSET
1
COMMENTS
Characteristic function of A063532, numbers k such that phi(k) + 1 = x^2 and sigma(k) + 1 = y^2 for some x and y.
LINKS
EXAMPLE
a(15) = 1 because both 1+phi(15) = 9 and 1+sigma(15) = 25 are squares.
MATHEMATICA
Table[If[AllTrue[{Sqrt[1+EulerPhi[n]], Sqrt[1+DivisorSigma[1, n]]}, IntegerQ], 1, 0], {n, 130}] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Dec 22 2018 *)
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Dec 08 2017
STATUS
approved