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 A240588 a(1) = 1, a(2) = 2; for n >= 3, a(n) = least number not included earlier that divides the concatenation of all previous terms. 11
 1, 2, 3, 41, 7, 9, 137131, 61, 2023244487101, 13, 19, 11, 143, 142733, 21, 17, 193, 37, 3907, 1290366811360047359, 1805030483980039, 3803623, 123, 369, 27, 23, 58271, 47609, 523, 79, 307, 179, 73, 57, 18032419296851, 29, 31, 3281881401611107, 69, 171, 60244474373, 197, 97 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS From Scott R. Shannon, Dec 19 2019: (Start) The next unknown term a(131) requires the factorization of a 517-digit composite number 46297...2963. (End) LINKS Scott R. Shannon, Table of n, a(n) for n = 1..130. EXAMPLE a(1)=1 and a(2)=2. a(1) U a(2) = 12 and its divisors are 1, 2, 3, 4, 6, 12. Therefore 3 is the least number not yet present in the sequence which divides 12. Again, a(1) U a(2) U a(3) = 123 and its divisors are 1, 3, 41, 123. Therefore a(4)=41. Etc. MAPLE with(numtheory): T:=proc(t) local x, y; x:=t; y:=0; while x>0 do x:=trunc(x/10); y:=y+1; od; end: P:=proc(q) local a, b, c, k, n; b:=12; print(1); print(2); c:=[1, 2]; for n from 1 to q do a:=sort([op(divisors(b))]); for k from 2 to nops(a) do if not member(a[k], c) then c:=[op(c), a[k]]; b:=a[k]+b*10^T(a[k]); print(a[k]); break; fi; od; od; end: P(19); MATHEMATICA a = {1, 2}; While[Length[a] < 22,   n = ToExpression[StringJoin[ToString /@ a]];   AppendTo[a, SelectFirst[Sort[Divisors[n]], FreeQ[a, #] &]] ]; a CROSSREFS Cf. A096097, A096098, A241811. Sequence in context: A242174 A340394 A288519 * A013646 A059800 A330293 Adjacent sequences:  A240585 A240586 A240587 * A240589 A240590 A240591 KEYWORD nonn,base AUTHOR Paolo P. Lava, Apr 29 2014 EXTENSIONS a(20)-a(40) from Alois P. Heinz, May 08 2014 a(22) corrected by Ryan Hitchman, Sep 14 2017 a(23)-a(25) from Robert Price, May 16 2019 a(23)-a(25) corrected, and a(26)-a(43) added by Scott R. Shannon, Dec 10 2019 STATUS approved

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Last modified April 22 14:09 EDT 2021. Contains 343177 sequences. (Running on oeis4.)