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%I #12 May 25 2015 18:33:08
%S 1,2,6,8,20,18,42,40,63,70,110,84,156,154,180,192,272,234,342,300,378,
%T 418,506,408,575,598,648,644,812,690,930,864,990,1054,1120,1008,1332,
%U 1330,1404,1320,1640,1470,1806,1716,1800,1978,2162,1872,2303,2250,2448
%N Define S(k) to be the sequence of divisors and multiples of k, e.g. S(1) = 1,2,3,4,5... S(2) = 1,2,4,6,8,10,... S(10) = 1,2,5,10,20,30,40,50,...; a(n) = n-th term of the n-th sequence S(n).
%H Ivan Neretin, <a href="/A069553/b069553.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = n*{n - d(n) + 1} where d(n) = number of divisors of n.
%t Table[n (n + 1 - DivisorSigma[0, n]), {n, 1, 51}] (* _Ivan Neretin_, May 25 2015 *)
%o (PARI) a(n) = n*(n - numdiv(n) + 1); \\ _Michel Marcus_, Sep 17 2013
%K nonn
%O 1,2
%A _Amarnath Murthy_, Mar 22 2002
%E Corrected and extended by _Ray Chandler_, Sep 29 2003