

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
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OFFSET

1,1


COMMENTS

A010051(a(n))*(1A156659(a(n))) = 1; subsequence of A156657.  Reinhard Zumkeller, Feb 18 2009
Also, primes p such that p1 is a nonsemiprime.  JuriStepan 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 (311)/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, A059452A059456, 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



