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A337308
Natural numbers that yield a coprime pair representing a proper fraction under the inverse of Cantor's pairing function.
0
8, 13, 18, 19, 26, 32, 33, 34, 41, 43, 50, 52, 53, 62, 64, 72, 73, 74, 75, 76, 85, 89, 98, 99, 100, 101, 102, 103, 114, 116, 118, 128, 131, 133, 134, 145, 147, 149, 151, 162, 163, 164, 165, 166, 167, 168, 169, 182, 184, 188, 200, 201, 202, 203, 204, 205, 206
OFFSET
1,1
COMMENTS
Equivalently: The image of the function f(x,y)=(x+y)*(x+y+1)/2+y for x,y coprime and 0 < x < y.
EXAMPLE
The fully reduced proper fraction 2/5 is mapped to 33 by Cantor's pairing function.
PROG
(Python) # Edited by M. F. Hasler, Mar 25 2023
from math import gcd
def A337308_first(N):
L, b = [], 0
f = lambda a: (a + b) * (a + b + 1) // 2 + b
while N > 0:
b += 1
if len(L) > 1:
L.sort()
while L and L[0] < f(1):
yield L.pop(0)
N -= 1
L.extend(f(a) for a in range(1, b) if gcd(a, b) == 1)
print(list(A337308_first(50)))
CROSSREFS
Superset of A277557.
Sequence in context: A006613 A204221 A348277 * A014134 A085989 A319879
KEYWORD
nonn
AUTHOR
Alexander Fraebel, Aug 22 2020
STATUS
approved