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 A018884 Squares using at most two distinct digits, not ending in 0. 3
 1, 4, 9, 16, 25, 36, 49, 64, 81, 121, 144, 225, 441, 484, 676, 1444, 7744, 11881, 29929, 44944, 55225, 69696, 9696996, 6661661161 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS No other terms below 10^41. The sequence is probably finite. The two distinct digits of a term cannot both be in the set {0,2,3,7,8}. Looking at the digits (with leading zeros) of i^2 mod 10^4 for 0 <= i < 10^4 shows that there are no repunit terms > 10 and the two distinct digits of a term must be one of the following 21 pairs: '01', '04', '09', '12', '14', '16', '18', '24', '25', '29', '34', '36', '45', '46', '47', '48', '49', '56', '67', '69', '89'. - Chai Wah Wu, Apr 06 2019 REFERENCES Richard K. Guy, Unsolved Problems in Number Theory, Section F24 (at p. 262) (Springer-Verlag, 2d ed. 1994). LINKS Table of n, a(n) for n=1..24. Eric Weisstein's World of Mathematics, Square Number. MATHEMATICA Flatten[Table[Select[Flatten[Table[FromDigits/@Tuples[{a, b}, n], {n, 10}]], IntegerQ[ Sqrt[#]]&], {a, 9}, {b, 9}]]//Union (* Harvey P. Dale, Sep 21 2018 *) CROSSREFS Cf. A000290, A016069, A016070, A018885. Sequence in context: A068854 A111704 A052041 * A050749 A096599 A016073 Adjacent sequences: A018881 A018882 A018883 * A018885 A018886 A018887 KEYWORD nonn,base,more,hard AUTHOR David W. Wilson STATUS approved

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Last modified August 9 16:51 EDT 2024. Contains 375044 sequences. (Running on oeis4.)