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A295233
Perfect n-th powers y^n (n >= 3) of the form x^2 + 2^a * 5^b (x, a, b >= 1, gcd(x, y) = 1).
1
81, 729, 1331, 6561, 68921, 161051, 2146689, 315821241
OFFSET
1,1
COMMENTS
Luca and Togbe showed that there are no other terms.
LINKS
F. Luca and A. Togbe, On the Diophantine Equation x^2 + 2^a 5^b y^n, Int. J. Number Theory 4 (2008), 973-979.
EXAMPLE
a(2) = 729 = 23^2 + 2^3 * 5^2 = 3^6 = 9^3, a(8) = 315821241 = 17771^2 + 2^9 * 5^2 = 681^3.
CROSSREFS
Sequence in context: A133549 A235946 A090257 * A271829 A066431 A206086
KEYWORD
nonn,fini,full
AUTHOR
Tomohiro Yamada, Nov 18 2017
STATUS
approved