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A280878 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) congruent to {3,9,21,27}(mod 30). 3
21, 33, 63, 99, 147, 189, 231, 273, 297, 357, 363, 399, 429, 441, 483, 561, 567, 609, 627, 651, 663, 693, 741, 759, 777, 819, 861, 891, 897, 903, 957, 969, 987, 1023, 1029, 1071, 1089, 1113, 1131, 1173, 1197, 1209, 1221, 1239, 1281, 1287, 1311, 1323, 1353, 1407, 1419, 1443, 1449 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Probability densities satisfying P(a(n)) < P(a(n)-1) and 1 <= m <= a(n), and a(n) congruent to 1(mod 2) and a(n) congruent to {3,9,21,27}(mod 30).

Subset of A280877.

Related to Euler phi function A000010 by P(n) = ((2*Sum_{m=1..a(n)} phi(m))-1)/a(n)^2.

LINKS

A.H.M. Smeets, Table of n, a(n) for n = 1..11142

PROG

(Python)

from fractions 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 and x%30 != 15):

........print(i, x)

........i = i + 1

....to = t

CROSSREFS

Sequence in context: A032603 A233562 A128283 * A033901 A033656 A270074

Adjacent sequences:  A280875 A280876 A280877 * A280879 A280880 A280881

KEYWORD

nonn

AUTHOR

A.H.M. Smeets, Jan 09 2017

STATUS

approved

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Last modified April 17 22:19 EDT 2021. Contains 343071 sequences. (Running on oeis4.)