OFFSET
1,2
EXAMPLE
Equivalently, this is row 4 of the array A[k,n] = n-th value of the sequence: list of pairs n,k*n, where n is the least unused number so far. That array begins:
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n...|.1..2..3..4..5..6..7..8..9..10..11..12..13..14..15..16..17..18..19..20
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k=2.|.1..2..3..6..4..8..5.10..7..14...9..18..11..22..12..24..13..26..15..30
k=3.|.1..3..2..6..4.12..5.15..7..21...8..24...9..27..10..30..11..33..13..39
k=4.|.1..4..2..8..3.12..5.20..6..24...7..28...9..36..10..40..11..44..13..52
k=5.|.1..5..2.10..3.15..4.20..6..30...7..35...8..40...9..45..11..55..12..60
k=6.|.1..6..2.12..3.18..4.24..5..30...7..42...8..48...9..54..10..60..11..66
k=7.|.1..7..2.14..3.21..4.28..5..35...6..42...8..56...9..63..10..70..11..77
k=8.|.1..8..2.16..3.24..4.32..5..40...6..48...7..56...9..72..10..80..11..88
k=9.|.1..9..2.18..3.27..4.36..5..45...6..54...7..63...8..72..10..90..11..99
k=10|.1.10..2.20..3.30..4.40..5..50...6..60...7..70...8..80...9..90..11.110
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MATHEMATICA
L = {1, 4}; Do[x=First[Complement[Range[Max[L] + 1], L]]; L = Join[L, {x, 4*x}], {38}]; L (* Giovanni Resta, Jun 19 2016 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Dec 28 2007
EXTENSIONS
Data corrected by Giovanni Resta, Jun 19 2016
STATUS
approved