login
A359864
a(n) is the number of solutions to the congruence x^y == y^x (mod n) where 0 <= x,y <= n.
0
4, 3, 4, 7, 8, 9, 18, 19, 18, 17, 22, 27, 30, 31, 28, 67, 40, 37, 60, 55, 52, 57, 80, 87, 64, 73, 108, 85, 78, 75, 102, 239, 74, 97, 74, 115, 102, 125, 110, 191, 108, 123, 118, 151, 140, 149, 162, 331, 134, 133, 128, 201, 184, 217, 178, 299, 202, 163, 178, 251
OFFSET
1,1
COMMENTS
a(n) is always greater than n.
FORMULA
a(n) = Sum_{x=0..n} Sum_{y=0..n} [x^y == y^x (mod n)].
PROG
(Python)
def a(n):
count = 0
for x in range(0, n + 1):
for y in range(0, n + 1):
if x == y or pow(x, y, n) == pow(y, x, n): count += 1
return count
(PARI) a(n) = sum(x=0, n, sum(y=0, n, Mod(x, n)^y == Mod(y, n)^x)); \\ Michel Marcus, Jan 16 2023
CROSSREFS
Cf. A355069.
Sequence in context: A200592 A021027 A289672 * A361849 A339409 A075246
KEYWORD
nonn
AUTHOR
Darío Clavijo, Jan 16 2023
STATUS
approved