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 A064951 Sum of lcm(x, y) for 1 <= x, y <= n. 2
 1, 7, 28, 72, 177, 303, 604, 948, 1497, 2127, 3348, 4272, 6313, 8119, 10324, 13060, 17701, 20995, 27512, 32132, 38453, 45779, 57440, 64664, 77689, 89935, 104704, 117948, 141525, 154755, 183616, 205472, 231113, 258959, 290564, 314720, 364041 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is also the entrywise 1-norm of the n X n LCM matrix. LINKS Harry J. Smith, Table of n, a(n) for n = 1..1000 FORMULA a(n) = a(n-1) + 2*A051193(n) - n = a(n-1) + n*A057660(n) = Sum_{1 <= i <= j <= n} (j^2/gcd(i, j)). - Henry Bottomley, Oct 29 2001 MATHEMATICA Table[nn = n; Total[Level[Table[Table[LCM[i, j], {i, 1, nn}], {j, 1, nn}], {2}]], {n, 1, 37}] (* Geoffrey Critzer, Jan 14 2015 *) PROG (PARI) { a=0; for (n=1, 1000, a+=n*sum(k=1, n, n/gcd(n, k)); write("b064951.txt", n, " ", a) ) } \\ Harry J. Smith, Oct 01 2009 CROSSREFS Cf. A018806. Sequence in context: A008457 A138503 A223765 * A296986 A211899 A073995 Adjacent sequences:  A064948 A064949 A064950 * A064952 A064953 A064954 KEYWORD nonn,changed AUTHOR Vladeta Jovovic, Oct 28 2001 STATUS approved

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Last modified March 18 19:00 EDT 2018. Contains 300772 sequences. (Running on oeis4.)