|
|
A067811
|
|
Numbers n such that phi(n)^2 + sigma(n)^2 is an integer square.
|
|
1
|
|
|
7, 32, 33, 41, 68, 145, 209, 237, 239, 266, 328, 372, 384, 385, 442, 522, 622, 905, 945, 1157, 1243, 1288, 1357, 1581, 1615, 1643, 1798, 1853, 1885, 1978, 1995, 2093, 2418, 2541, 2698, 2765, 2769, 2981, 3013, 3161, 3315, 3451, 3519, 3577, 4041, 4309, 4318
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
phi(32)^2 + sigma(32)^2 = 16^2 + 63^2 = 4225 = 65^2, so 32 is a term of the sequence.
|
|
MATHEMATICA
|
Select[Range[10^4], IntegerQ[Sqrt[EulerPhi[ # ]^2 + DivisorSigma[1, # ]^2]] &]
|
|
PROG
|
(PARI) isok(n) = issquare(eulerphi(n)^2+sigma(n)^2); \\ Michel Marcus, Aug 13 2019
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|