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A258373
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a(n+1) is the least number not occurring earlier such that concatenation(a(n),a(n+1)) - 1 is a palindrome; a(1)=1.
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2
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 102, 202, 203, 303, 304, 404, 405, 505, 506, 606, 607, 707, 708, 808, 809, 909, 910, 20, 103, 302, 204, 403, 305, 504, 406, 605, 507, 706, 608, 807, 709, 908, 810, 19, 92, 30, 104, 402, 205, 503, 306, 604, 407, 705, 508, 806, 609, 907, 710, 18
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OFFSET
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1,2
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LINKS
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EXAMPLE
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The concatenation of the first two terms is 12, and
12 - 1 = 11 is a palindrome, and similar for all subsequent terms:
23 - 1 = 22,
34 - 1 = 33,
...
910 - 1 = 909,
10102 - 1 = 10101,
...
9230 - 1 = 9229 is a palindrome, ...
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PROG
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(PARI) {S=[a=1]; for(i=1, 100, print1(a", "); for(k=1, 9e9, Vecrev(d=digits(eval(Str(a, k))-1))==d||next; setsearch(S, k)&&next; S=setunion(S, [a=k]); break))}
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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