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A087502
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Smallest positive integer which when written in base n is doubled when the last digit is put first.
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2
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32, 18, 8, 10993850, 2129428800, 21, 5064320, 105263157894736842, 40, 64609423538, 5712, 65, 58774271029236501660840264682112, 67650, 96, 833, 586081355679130611935159482937228562988190880, 133
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OFFSET
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3,1
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COMMENTS
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a(n) is the smallest integer of the form x*(n^d-1)/(2n-1) for integer x and d, where 1 < x < n and d > 1. x is the last digit and d is the number of digits of a(n) in base n. - Pontus von Brömssen, Jan 06 2019
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LINKS
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Pontus von Brömssen, Table of n, a(n) for n = 3..221
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EXAMPLE
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a(10) = 105263157894736842 because 2*105263157894736842 = 210526315789473684 and no smaller number has this property. (Leading zeros are not allowed, otherwise 2*052631578947368421 = 105263157894736842 would be a smaller solution.)
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MAPLE
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A087502 := proc(n) local d, a; d := 1; a := n; while a>=n do d := d+1; a := denom((2^d-1)/(2*n-1)); od; return(max(2, a)*(n^d-1)/(2*n-1)); end proc;
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CROSSREFS
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See A158877 for these numbers written in base n. Cf. A023094, A034089, A081463, A087502.
Sequence in context: A033352 A140387 A023094 * A070628 A147514 A291155
Adjacent sequences: A087499 A087500 A087501 * A087503 A087504 A087505
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KEYWORD
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nonn,base
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AUTHOR
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Pontus von Brömssen, Sep 10 2003
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STATUS
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approved
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