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 A261138 The concatenation of 123456...n and reverse of this number. 0
 11, 1221, 123321, 12344321, 1234554321, 123456654321, 12345677654321, 1234567887654321, 123456789987654321, 1234567891001987654321, 12345678910111101987654321, 123456789101112211101987654321, 1234567891011121331211101987654321 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are palindromic numbers by construction. Starts as A259937, but A259937 generates non-palindromic terms at n>9. LINKS FORMULA a(n) = concatenate( A007908(n), A138793(n) leading zeros kept). MATHEMATICA Table[d = Flatten[IntegerDigits /@ Range@ n]; FromDigits@ Flatten[{d, Reverse@ d}], {n, 13}] (* Michael De Vlieger, Aug 20 2015 *) CROSSREFS Cf. A259937, A002477. Sequence in context: A233012 A019524 A274766 * A259937 A078269 A015009 Adjacent sequences:  A261135 A261136 A261137 * A261139 A261140 A261141 KEYWORD nonn,base AUTHOR Umut Uludag, Aug 10 2015 STATUS approved

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Last modified October 21 00:56 EDT 2017. Contains 293679 sequences.