|
|
A280879
|
|
Occurrences of decrease of the probability density P(n) of coprime numbers k,m, satisfying 1 <= k <= a(n) and 1 <= m <= a(n), and a(n) congruent to 1 (mod 2) and a(n) not congruent to 3 (mod 6).
|
|
3
|
|
|
5005, 6545, 7315, 7735, 8645, 8855, 10465, 11165, 11935, 14245, 25025, 32725, 35035, 36575, 38675, 43225, 44275, 45815, 51205, 52325, 54145, 55055, 55825, 59675, 60515, 61985, 65065, 71225, 71995, 73255, 78155, 80465, 83545, 85085, 95095, 97405, 99715
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Probability densities satisfying P(a(n)) < P(a(n)-1) and a(n) congruent to 1 (mod 2) and a(n) not congruent to 3 (mod 6).
It appears that most numbers satisfy a(n) congruent to 35 (mod 70), but a(74) congruent to 15 (mod 70) and a(93) congruent to 55 (mod 70).
P(n) = ((2*Sum_{m=1..a(n)} phi(m))-1)/a(n)^2 (Cf. Euler phi function A000010).
|
|
LINKS
|
|
|
PROG
|
(Python)
from fraction import gcd
t = 1
to = 1
i = 1
x = 1
while x > 0:
....x = x + 1
....y = 0
....while y < x:
........y = y + 1
........if gcd(x, y) == 1:
............t = t + 2
....e = t*(x-1)*(x-1) - to*x*x
....if (e < 0 and x%2 == 1 and x%6 != 3):
........print(i, x)
........i = i + 1
....to = t
(PARI) P(n) = (2 *sum(j=1, n, eulerphi(j)) - 1)/n^2;
isok(n) = (n % 2) && ((n % 6) != 3) && (P(n) < P(n-1)); \\ Michel Marcus, Jan 29 2017
(Python)
from sympy import totient
n += 1
h = totient(n)
t2 = t+h
if n % 2 and n % 6 != 3 and 2*(n*(h*n - 2*t2 + 1) + t2) < 1:
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|