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 A059456 Unsafe primes: primes not in A005385. 16
 2, 3, 13, 17, 19, 29, 31, 37, 41, 43, 53, 61, 67, 71, 73, 79, 89, 97, 101, 103, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 173, 181, 191, 193, 197, 199, 211, 223, 229, 233, 239, 241, 251, 257, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A010051(a(n))*(1-A156659(a(n))) = 1; subsequence of A156657. - Reinhard Zumkeller, Feb 18 2009 Also, primes p such that p-1 is a non-semiprime. - Juri-Stepan Gerasimov, Apr 28 2010 Conjecture: From the sequence of prime numbers, let 2 and remove the first data iteration of 2*p+1; leave 3 and remove the prime data by the iteration 2*p+1 and we get the sequence. Example for p=2, remove(5,11,23,47); p=3, remove(7); p=13, p=17, p=19, p=23, remove(47); and so on. - Vincenzo Librandi, Aug 07 2010 LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 EXAMPLE 31 is here because (31-1)/2=15 is not prime. 2 and 3 are here because 1/2 and 1 are not prime numbers. MATHEMATICA Complement[Prime@ Range@ PrimePi@ Max@ #, #] &@ Select[Prime@ Range@ 90, PrimeQ[(# - 1)/2] &] (* Michael De Vlieger, May 01 2016 *) Select[Prime[Range[100]], PrimeOmega[#-1]!=2&] (* Harvey P. Dale, May 13 2018 *) PROG (PARI) is(n)=isprime(n) && !isprime(n\2) \\ Charles R Greathouse IV, May 02 2016 CROSSREFS Cf. A005384, A005385, A053176, A059452-A059456, A007700, A005602, A023272, A023302, A023330. Sequence in context: A299543 A059670 A038975 * A274589 A019394 A048704 Adjacent sequences:  A059453 A059454 A059455 * A059457 A059458 A059459 KEYWORD nonn AUTHOR Labos Elemer, Feb 02 2001 STATUS approved

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Last modified August 16 16:40 EDT 2018. Contains 313809 sequences. (Running on oeis4.)