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A088798
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Numbers n that divide the concatenation of n-1, n-2 and n-3.
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12
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3, 19, 57, 3276457, 9829371, 22997937, 24687460011, 24504559526049, 1152870338086169, 3458611014258507, 19831522709797616449, 54128285729329681609, 59494568129392849347, 61582096835687335289
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OFFSET
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1,1
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COMMENTS
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Each member of this sequence also appears to be a divisor of the number formed when concatenating (n+1), (n+2) and (n+3) in that order. Each nonprime member of the terms above appears to be divisible by 3. Further note that apart from 3 itself, if a(n) is a prime, then 3 * a(n) also appears to be a member. 19*3=57, 3276457*3=9829371. More prime members would need to be found to test this.
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LINKS
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EXAMPLE
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a(2)=19 because 19 is a divisor of 181716. a(4)=3276457 because 3276457 is a divisor of 327645632764553276454.
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MAPLE
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prevcatOld := proc(n, t, o) local i, s; s := ""; for i from 1 to t do if o="a" then s := cat(convert(n-i, string), s) else s := cat(s, convert(n-i, string)) fi; od; parse(s) end; nextdivcat := proc(startAt, endAt, numTerms, catOrder) local i; for i from startAt to endAt while (prevcatOld(i, numTerms, catOrder) mod i > 0) do od; if i<=endAt then i else -1 fi; end; s := NULL; t := 2; for j from 1 to 10 do t := nextdivcat(t+1, 23000000, 3, "d"); s := s, t od; print(s);
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MATHEMATICA
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Do[ If[ Mod[ FromDigits[ Join[ IntegerDigits[2n], IntegerDigits[2n - 1], IntegerDigits[2n - 2]]], (2n + 1)] == 0, Print[2n + 1]], {n, 1, 700000000}]
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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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Chuck Seggelin (barkeep(AT)plastereddragon.com), Oct 19 2003
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EXTENSIONS
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STATUS
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approved
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