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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..1000 EXAMPLE 225 = 15^2 is a square, and becomes the square 7225 = 85^2 if prefixed with a 7. MAPLE P:=proc(i) local a, n; for n from 1 by 1 to i do a:=7*10^floor(1+log10(n^2))+n^2; if a=trunc(sqrt(a))^2 then print(n^2); fi; od; end: P(10000000000000); # Paolo P. Lava, Nov 02 2009 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 Adjacent sequences:  A167039 A167040 A167041 * A167043 A167044 A167045 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

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Last modified May 25 17:48 EDT 2022. Contains 354071 sequences. (Running on oeis4.)