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1,3
It is conjectured that there are no other terms.
There are no further terms below 10^10000.
Mauldin, R. Daniel; Ulam, S. M.; Mathematical problems and games. Adv. in Appl. Math. 8 (1987), 281-344.
C. Pomerance, Divisors of the middle binomial coefficient, Amer. Math. Monthly, 112 (2015), 636-644.
Table of n, a(n) for n=1..3.
Sequence in context: A252215 A250760 A184452 * A252636 A068266 A140350
Adjacent sequences: A151747 A151748 A151749 * A151751 A151752 A151753
nonn,bref
N. J. A. Sloane, Jul 30 2009
approved