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
KEYWORD
base,nonn
AUTHOR
Eric Angelini and Carole Dubois, Jun 09 2021
STATUS
approved