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A345142
The product of two successive terms is always even, and so is the product of two successive digits. Lexicographically earliest sequence of distinct positive terms with this property.
0
1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 10, 12, 14, 16, 18, 21, 22, 23, 24, 25, 26, 27, 28, 29, 40, 30, 32, 34, 36, 38, 41, 42, 43, 44, 45, 46, 47, 48, 49, 60, 50, 52, 54, 56, 58, 61, 62, 63, 64, 65, 66, 67, 68, 69, 80, 70, 72, 74, 76, 78, 81, 82, 83, 84, 85, 86, 87, 88, 89, 200, 90, 92, 94, 96, 98, 100, 101, 201
OFFSET
1,2
EXAMPLE
a(9) = 9 and a(10) = 20; we have 9 * 20 = 180 (even), 9 * 2 = 18 (even) and 2 * 0 = 0 (even).
MATHEMATICA
a[1]=1; a[n_]:=a[n]=(k=1; While[OddQ[a[n-1]k]||(!And@@EvenQ[Times@@@Subsequences[Flatten[IntegerDigits/@{a[n-1], k}], {2}]])||MemberQ[Array[a, n-1], k], k++]; k); Array[a, 100] (* Giorgos Kalogeropoulos, Jun 09 2021 *)
CROSSREFS
Cf. A344543.
Sequence in context: A048410 A341161 A180083 * A275775 A358129 A217556
KEYWORD
base,nonn
AUTHOR
Eric Angelini and Carole Dubois, Jun 09 2021
STATUS
approved