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A018806 Sum of gcd(x, y) for 1 <= x, y <= n. 3
1, 5, 12, 24, 37, 61, 80, 112, 145, 189, 220, 288, 325, 389, 464, 544, 593, 701, 756, 880, 989, 1093, 1160, 1336, 1441, 1565, 1700, 1880, 1965, 2205, 2296, 2488, 2665, 2829, 3028, 3328, 3437, 3621, 3832, 4152, 4273, 4621, 4748, 5040, 5373, 5597, 5736, 6168 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

COMMENTS

a(n) is also the entrywise 1-norm of the n*n GCD matrix.

FORMULA

Sum_{k=1..n} phi(k)*(floor(n/k))^2. - Vladeta Jovovic (vladeta(AT)eunet.rs), Nov 10 2002

CROSSREFS

Cf. A000010, A018805, A064951.

Sequence in context: A066869 A023172 A100479 * A191831 A188182 A187210

Adjacent sequences:  A018803 A018804 A018805 * A018807 A018808 A018809

KEYWORD

nonn

AUTHOR

David W. Wilson (davidwwilson(AT)comcast.net)

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Last modified February 17 19:13 EST 2012. Contains 206085 sequences.