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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.)