A111175 Numbers n such that 30*n + 1 is prime.

1, 2, 5, 6, 7, 8, 9, 11, 14, 18, 19, 20, 21, 22, 23, 25, 27, 33, 34, 35, 39, 40, 41, 43, 44, 46, 49, 51, 54, 58, 60, 61, 62, 65, 67, 71, 72, 74, 75, 76, 77, 78, 79, 84, 85, 89, 91, 93, 95, 99, 100, 102, 104, 106, 109, 110, 111, 112, 113, 117, 118, 119, 121, 123, 131, 134, 135

Offset: 1

Author

Parthasarathy Nambi, Oct 21 2005

Keywords

• nonn

Comments

Encoded primes with LSD 1 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. Example: 2671, with LSD 1 and (SOD-1)/3 = 2 (integer); Then 2671/30 = 89.033, or 89, which is in the sequence, and thus 2671 is prime. - Ki Punches, Mar 18 2009

Examples

			If n=99 then 30*n + 1 = 2971 (prime).
		

Crossrefs

Cf. A158573, A158614, A158648, A158746, A158791, A158806, A158850.

Programs

PARI

is(n)=isprime(30*n+1) \\ Charles R Greathouse IV, Feb 17 2017

Formula

a(n) = (A132230(n) - 1)/30 = Floor[A132230(n)/30]. - Chandler

Extensions

Extended by Ray Chandler, Apr 07 2009