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A068520
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Numbers n which can be transformed into a true arithmetic statement by inserting zero or more parentheses and elementary arithmetic operators ((, ), +, -, *, /) and one equality sign (=) as the rightmost insertion into the decimal representation of n.
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1
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11, 22, 33, 44, 55, 66, 77, 88, 99, 100, 101, 110, 111, 112, 122, 123, 133, 134, 144, 145, 155, 156, 166, 167, 177, 178, 188, 189, 199, 200, 202, 211, 212, 213, 220, 221, 224, 235, 236, 246, 248, 257, 268, 279, 300, 303, 312, 313, 314, 321, 325, 326, 330, 331
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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The minus sign is considered only as two-place infix operator, not as one-place prefix operator. Therefore -1 + 2 = 1 is not allowed and 121 is not a term.
These numbers are called (elementary) "didactic numbers".
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LINKS
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EXAMPLE
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7 = 7; 1 * 0 = 0; 2 - 2 = 0; 2 / 2 = 1; 18 / 2 = 9; 2 * (3 + 4) = 14. Therefore 77, 100, 220, 221, 1829 and 23414 are terms of the sequence.
2 - 1 = 1, therefore 211 is a term of the sequence. - Sean A. Irvine, Feb 21 2024
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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More terms from Larry Reeves (larryr(AT)acm.org), Jun 21 2002
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STATUS
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approved
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