OFFSET
1,1
FORMULA
EXAMPLE
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.
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.
MATHEMATICA
Table[DivisorSigma[1, n]*Prime[n], {n, 1, 50}] (* G. C. Greubel, Apr 27 2016 *)
PROG
(PARI) a(n) = prime(n)*sigma(n); \\ Michel Marcus, Apr 27 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Apr 26 2016
STATUS
approved