OFFSET
1,1
FORMULA
a(n) = (6n-5)*isprime(6n-5) + (6n-1)*isprime(6n-1), where isprime = A010051. - M. F. Hasler, Jun 15 2008
EXAMPLE
6*11 - 5 = 61 is prime, but 6*11 - 1 = 65 is not prime, so a(11) = 61.
MAPLE
a:= n-> add(i, i=select(isprime, [6*n-5, 6*n-1])):
seq(a(n), n=1..59); # Alois P. Heinz, May 18 2021
PROG
(PARI) a(n)=(6*n-5)*isprime(6*n-5)+(6*n-1)*isprime(6*n-1) \\ M. F. Hasler, Jun 15 2008
(Python)
from sympy import isprime
def a(n): return sum(k*isprime(k) for k in {6*n-5, 6*n-1})
print([a(n) for n in range(1, 60)]) # Michael S. Branicky, May 18 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Jun 10 2008
EXTENSIONS
Edited by M. F. Hasler, Jun 15 2008
a(52) corrected and a(58) deleted by Michael S. Branicky, May 18 2021
STATUS
approved