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a(n) = b(n)th integer among those positive integers not yet occurring in {a(k)}, where {b(k)} is the concatenation of the divisors of the positive integers.
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%I #18 Apr 20 2022 09:57:09

%S 1,2,4,3,7,5,8,11,6,14,9,12,15,19,10,22,13,17,21,27,16,23,31,18,24,29,

%T 36,20,39,25,28,32,34,38,46,26,49,30,35,44,54,33,41,45,59,37,42,48,55,

%U 65,40,68,43,50,52,58,63,75,47,78,51,56,61,64,72,85,53,62,71,90,57,66

%N a(n) = b(n)th integer among those positive integers not yet occurring in {a(k)}, where {b(k)} is the concatenation of the divisors of the positive integers.

%C b(n) = A027750(n). {a(n)} is a permutation of the positive integers.

%H Rémy Sigrist, <a href="/A120619/b120619.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>

%e The first 6 terms of {a(k)} are 1,2,4,3,7,5. So the positive integers not occurring among these terms are 6,8,9,10,... The 7th term of A027750 is 2. So a(7) = 8.

%o (PARI) { val = List([1..90]); n = 0; for (m=1, oo, fordiv (m, d, v = val[d]; listpop(val, d); print1 (v", "); if (n++==72, break (2)))) } \\ _Rémy Sigrist_, Apr 20 2022

%Y Cf. A027750, A120620.

%K nonn

%O 1,2

%A _Leroy Quet_, Jun 18 2006

%E Extended by _Ray Chandler_, Jun 19 2006

%E Edited by _Charles R Greathouse IV_, Apr 27 2010