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A088798 Numbers n that divide the concatenation of n-1, n-2 and n-3. 12
3, 19, 57, 3276457, 9829371, 22997937, 24687460011, 24504559526049, 1152870338086169, 3458611014258507, 19831522709797616449, 54128285729329681609, 59494568129392849347, 61582096835687335289 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

a(2)=19 because 19 is a divisor of 181716. a(4)=3276457 because 3276457 is a divisor of 327645632764553276454.

MAPLE

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);

MATHEMATICA

Do[ If[ Mod[ FromDigits[ Join[ IntegerDigits[2n], IntegerDigits[2n - 1], IntegerDigits[2n - 2]]], (2n + 1)] == 0, Print[2n + 1]], {n, 1, 700000000}]

CROSSREFS

Cf. A069860, A069862, A069871, A088797.

Sequence in context: A100697 A134268 A322209 * A027272 A164132 A106875

Adjacent sequences:  A088795 A088796 A088797 * A088799 A088800 A088801

KEYWORD

base,nonn

AUTHOR

Chuck Seggelin (barkeep(AT)plastereddragon.com), Oct 19 2003

EXTENSIONS

Edited by Robert G. Wilson v, Oct 20 2003

More terms from David Wasserman, Aug 25 2005

STATUS

approved

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Last modified August 21 06:14 EDT 2019. Contains 326162 sequences. (Running on oeis4.)