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A167042
Squares that remain squares when prefixed with a 7.
3
225, 5625, 22500, 562500, 2250000, 6125625, 19580625, 56250000, 225000000, 612562500, 1958062500, 2562890625, 5625000000, 22500000000, 51472265625, 61256250000, 195806250000, 256289062500, 562500000000, 2250000000000, 5147226562500, 6125625000000
OFFSET
1,1
EXAMPLE
225 = 15^2 is a square, and becomes the square 7225 = 85^2 if prefixed with a 7.
MATHEMATICA
Select[Range[25*10^5]^2, IntegerQ[Sqrt[#+7*10^IntegerLength[#]]]&] (* Harvey P. Dale, Mar 02 2015 *)
CROSSREFS
Sequence in context: A330819 A297760 A167035 * A242268 A164763 A164752
KEYWORD
nonn,base
AUTHOR
Claudio Meller, Oct 27 2009
EXTENSIONS
Keyword:base added by R. J. Mathar, Oct 28 2009
More terms from Chai Wah Wu, Sep 11 2014
STATUS
approved