1,1

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.

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

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);

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

Cf. A069860, A069862, A069871, A088797.

Sequence in context: A112627 A100697 A134268 this_sequence A027272 A106875 A041015

Adjacent sequences: A088795 A088796 A088797 this_sequence A088799 A088800 A088801

base,nonn

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

Edited by Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 20 2003

More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Aug 25 2005