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 A109931 Least palindromic multiple of concatenation n,n-1,...,3,2,1,2,3,...,n-1,n, or zero if no such multiple exists. a(n) is not equal to n. 1
 2, 424, 64246, 8642468, 5975335795, 65497555579456, 765439777777934567, 8765432999999992345678, 76606769668830703886696760667, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The multipliers are: 2, 2, 2, 2, 11, 1001, 100001, 10000001, ... Such a multiple may fail to exist for n >= 10 because the concatenation n,n-1,...,3,2,1,2,3,...,n-1,n is no longer a palindrome itself in that case (e.g., for n=10 the concatenation is 109876543212345678910). - Nathaniel Johnston, Jun 26 2011 LINKS EXAMPLE a(5) = 5975335795 = 11*543212345. MAPLE read(transforms): A109931 := proc(n) local k, m, v: m:=parse(cat(digrev(parse(cat(\$(1..n)))), cat(\$(2..n)))): for k from 2 do v:=k*m: if(v=digrev(v))then return v: fi: od: end: seq(A109931(n), n=2..6); # only valid for n <= 9, Nathaniel Johnston, Jun 26 2011 CROSSREFS Sequence in context: A154541 A119120 A332142 * A352498 A326364 A200951 Adjacent sequences: A109928 A109929 A109930 * A109932 A109933 A109934 KEYWORD base,more,nonn AUTHOR Amarnath Murthy, Jul 18 2005 EXTENSIONS a(6)-a(8) from Lars Blomberg, Jun 26 2011 a(9)-a(10) from Donovan Johnson, Oct 13 2011 STATUS approved

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Last modified February 2 15:30 EST 2023. Contains 360022 sequences. (Running on oeis4.)