A158573 Numbers k such that 30*k + 7 is prime.

0, 1, 2, 3, 4, 5, 9, 10, 11, 12, 13, 15, 16, 18, 19, 20, 24, 25, 26, 29, 30, 31, 32, 33, 36, 37, 41, 43, 44, 48, 52, 53, 54, 55, 58, 59, 62, 66, 67, 71, 76, 78, 79, 81, 82, 85, 87, 88, 89, 90, 92, 93, 95, 96, 97, 101, 102, 106, 107, 110, 115, 117, 118, 120, 121, 123, 124, 128

Offset: 1

Author

Ki Punches, Mar 21 2009

Keywords

• nonn

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.

Examples

			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.
		

Crossrefs

Cf. A111175, A158614, A158648, A158746, A158791, A158806, A158850.

Programs

Mathematica

Select[Range[0,200],PrimeQ[30#+7]&] (* Harvey P. Dale, Jul 20 2018 *)

PARI

is(n)=isprime(30*n+7) \\ Charles R Greathouse IV, Mar 07 2016

Formula

a(n) = (A132231(n) - 7)/30 = floor(A132231(n)/30). - Ray Chandler, Apr 07 2009

a(n) ~ (4/15) n log n. - Charles R Greathouse IV, Mar 07 2016

Extensions

Edited by Ray Chandler, Apr 07 2009