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Product of n-th prime and the sum of the divisors of n.
3

%I #21 Apr 28 2016 21:44:43

%S 2,9,20,49,66,156,136,285,299,522,372,1036,574,1032,1128,1643,1062,

%T 2379,1340,2982,2336,2844,1992,5340,3007,4242,4120,5992,3270,8136,

%U 4064,8253,6576,7506,7152,13741,5966,9780,9352,15570,7518,17376,8404,16212,15366,14328,10128,27652,12939,21297,16776,23422

%N Product of n-th prime and the sum of the divisors of n.

%F a(n) = prime(n)*sigma(n) = A000040(n)*A000203(n).

%F a(n) = sigma(n*prime(n)) - sigma(n) = A000203(n*A000040(n)) - A000203(n) = A000203(A033286(n)) - A000203(n) = A272173(n) - A000203(n).

%e For n = 9 the 9th prime is 23, and the sum of the divisors of 9 is 1 + 3 + 9 = 13, and 23*13 = 299, so a(9) = 299.

%e On the other hand 9*23 = 207 and the sum of the divisors of 207 is 1 + 3 + 9 + 23 + 69 + 207 = 312 and 312 - 13 = 299, so a(9) = 299.

%t Table[DivisorSigma[1, n]*Prime[n], {n, 1, 50}] (* _G. C. Greubel_, Apr 27 2016 *)

%o (PARI) a(n) = prime(n)*sigma(n); \\ _Michel Marcus_, Apr 27 2016

%Y Main diagonal of A272214.

%Y Cf. A000040, A000203, A033286, A272173, A272400.

%K nonn

%O 1,1

%A _Omar E. Pol_, Apr 26 2016