OFFSET
2,1
COMMENTS
Other known values: a(43) = 24458112 and a(47) = 3076480.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 2..59
Thomas Bloom, Problem 1063, Erdős Problems.
PROG
(SageMath)
def a(n):
m=2*n;
while 0<1:
t=binomial(m, n); S=[i for i in range(0, n) if t%(m-i)!=0];
if len(S)==1: return m;
else: m+=1
(PARI) isok(m, n) = my(b=binomial(m, n), nb=0); for (i=0, n-1, if (!(b % (m-i)), nb++)); nb==n-1;
a(n) = my(m=2*n); while (!isok(m, n), m++); m; \\ Michel Marcus, Oct 09 2025
(Python)
from itertools import count
from math import comb
def A389360(n):
c = comb(n<<1, n)
for m in count(n<<1):
s = 0
for i in range(n):
if c%(m-i):
s += 1
if s>1:
break
if s==1:
return m
c = c*(m+1)//(m+1-n) # Chai Wah Wu, Oct 14 2025
CROSSREFS
KEYWORD
nonn
AUTHOR
Stijn Cambie, Oct 01 2025
EXTENSIONS
a(38)-a(40) from Chai Wah Wu, Oct 14 2025
a(41) from Stijn Cambie, Oct 01 2025
STATUS
approved
