OFFSET
1,3
COMMENTS
Encoded primes with LSD 7 and (SOD-1)/3 integer, (LSD, least significant digit; SOD, sum of digits). Divide any such number by 30, if the whole number portion of the quotient is in the sequence, the number is prime.
FORMULA
a(n) ~ (4/15) n log n. - Charles R Greathouse IV, Mar 07 2016
EXAMPLE
Example: 3877, with LSD 7 and (SOD-1)/3 = 23 (integer); Then 3877/30 = 129.233, or 129, which is in the sequence, and thus 3877 is prime.
MATHEMATICA
Select[Range[0, 200], PrimeQ[30#+7]&] (* Harvey P. Dale, Jul 20 2018 *)
PROG
(PARI) is(n)=isprime(30*n+7) \\ Charles R Greathouse IV, Mar 07 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Ki Punches, Mar 21 2009
EXTENSIONS
Edited by Ray Chandler, Apr 07 2009
STATUS
approved