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A081091
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Primes of the form 2^i + 2^j + 1, i > j > 0.
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19
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7, 11, 13, 19, 37, 41, 67, 73, 97, 131, 137, 193, 521, 577, 641, 769, 1033, 1153, 2053, 2081, 2113, 4099, 4129, 8209, 12289, 16417, 18433, 32771, 32801, 32833, 40961, 65539, 133121, 147457, 163841, 262147, 262153, 262657, 270337, 524353, 524801
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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EXAMPLE
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7 = 2^2 + 2^1 + 1
11 = 2^3 + 2^1 + 1
13 = 2^3 + 2^2 + 1
19 = 2^4 + 2^1 + 1
37 = 2^5 + 2^2 + 1
41 = 2^5 + 2^3 + 1
67 = 2^6 + 2^1 + 1
73 = 2^6 + 2^3 + 1
97 = 2^6 + 2^5 + 1
131 = 2^7 + 2^1 + 1
137 = 2^7 + 2^3 + 1
193 = 2^7 + 2^6 + 1
521 = 2^9 + 2^3 + 1
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MAPLE
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N:= 20: # to get all terms < 2^N
select(isprime, [seq(seq(2^i+2^j+1, j=1..i-1), i=1..N-1)]); # Robert Israel, May 17 2016
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MATHEMATICA
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Select[Flatten[Table[2^i + 2^j + 1, {i, 21}, {j, i-1}]], PrimeQ] (* Alonso del Arte, Jan 11 2011 *)
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PROG
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(PARI) do(mx)=my(v=List(), t); for(i=2, mx, for(j=1, i-1, if(ispseudoprime(t=2^i+2^j+1), listput(v, t)))); Vec(v) \\ Charles R Greathouse IV, Jan 02 2014
(PARI) A81091=[7]; next_A081091(p, i=exponent(p), j=exponent(p-2^i))=!until(isprime(2^i+2^j+1), j++>=i && i++ && j=1)+2^i+2^j)
(Haskell)
a081091 n = a081091_list !! (n-1)
a081091_list = filter ((== 1) . a010051') a014311_list
(Python)
from itertools import count, islice
from sympy import isprime
from sympy.utilities.iterables import multiset_permutations
def A081091_gen(): # generator of terms
return filter(isprime, map(lambda s:int('1'+''.join(s)+'1', 2), (s for l in count(1) for s in multiset_permutations('0'*(l-1)+'1'))))
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CROSSREFS
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Cf. A095077 (primes with four bits set).
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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