OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = 3*prime(n) + 3 for n > 1. - Charles R Greathouse IV, Nov 22 2014
EXAMPLE
For n = 4 the 4th prime is 7 so the 4th even semiprime is 2*7 = 14. The sum of the divisors of 14 is 1 + 2 + 7 + 14 = 24, so a(4) = 24.
MATHEMATICA
DivisorSigma[1, #]&/@Select[Range[2, 500, 2], PrimeOmega[#]==2&] (* Harvey P. Dale, Jan 09 2015 *)
Join[{7}, Rest[3 Prime[Range[5000]] + 3]] (* Vincenzo Librandi, Jan 09 2018 *)
PROG
(PARI) v=3*apply(k->k+1, primes(100)); v[1]=7; v \\ Charles R Greathouse IV, Nov 22 2014
(Magma) [7] cat [3*NthPrime(n)+3: n in [2..60]]; // Vincenzo Librandi, Jan 09 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Nov 21 2014
STATUS
approved