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 A158573 Numbers k such that 30*k + 7 is prime. 9
 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 (list; graph; refs; listen; history; text; internal format)
 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. LINKS 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 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 Cf. A111175, A158614, A158648, A158746, A158791, A158806, A158850. Sequence in context: A037472 A096304 A119955 * A194398 A047603 A047362 Adjacent sequences:  A158570 A158571 A158572 * A158574 A158575 A158576 KEYWORD nonn AUTHOR Ki Punches, Mar 21 2009 EXTENSIONS Edited by Ray Chandler, Apr 07 2009 STATUS approved

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Last modified June 13 22:55 EDT 2021. Contains 345016 sequences. (Running on oeis4.)