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A080823

a(n)=n for n<=4; for n>4, a(n) is the smallest integer greater than a(n-1) that shares common factors with some (i.e., at least one) but not all of previous 4 terms.

1, 2, 3, 4, 6, 8, 9, 10, 14, 15, 16, 21, 22, 25, 26, 27, 28, 32, 33, 34, 35, 36, 38, 39, 40, 44, 45, 46, 51, 52, 55, 56, 57, 58, 62, 63, 64, 68, 69, 70, 74, 75, 76, 77, 78, 80, 81, 82, 85, 86, 87, 88, 92, 93, 94, 98, 99, 100, 104, 105, 106, 111, 112, 115, 116, 117, 118, 122

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OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

FORMULA

For n >= 119, a(n) = a(n-113) + 210. - Robert Israel, Dec 21 2016

MAPLE

for n from 1 to 4 do A[n]:= n od:

for n from 5 to 100 do

for k from A[n-1]+1 do

L:= map(igcd, [seq(A[i], i=n-4..n-1)], k);