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A158573 Numbers k such that 30*k + 7 is prime. 9

%I

%S 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,

%T 37,41,43,44,48,52,53,54,55,58,59,62,66,67,71,76,78,79,81,82,85,87,88,

%U 89,90,92,93,95,96,97,101,102,106,107,110,115,117,118,120,121,123,124,128

%N Numbers k such that 30*k + 7 is prime.

%C 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.

%F a(n) = (A132231(n) - 7)/30 = floor(A132231(n)/30). - _Ray Chandler_, Apr 07 2009

%F a(n) ~ (4/15) n log n. - _Charles R Greathouse IV_, Mar 07 2016

%e 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.

%t Select[Range[0,200],PrimeQ[30#+7]&] (* _Harvey P. Dale_, Jul 20 2018 *)

%o (PARI) is(n)=isprime(30*n+7) \\ _Charles R Greathouse IV_, Mar 07 2016

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

%K nonn

%O 1,3

%A _Ki Punches_, Mar 21 2009

%E Edited by _Ray Chandler_, Apr 07 2009

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Last modified July 26 16:44 EDT 2021. Contains 346294 sequences. (Running on oeis4.)