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A288305
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Pairs of a prime number and square of prime number differs by 2. (Pseudo-twin).
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1
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2, 4, 7, 9, 9, 11, 23, 25, 47, 49, 167, 169, 359, 361, 839, 841, 1367, 1369, 1847, 1849, 2207, 2209, 3719, 3721, 5039, 5041, 7919, 7921, 10607, 10609, 11447, 11449, 16127, 16129, 17159, 17161, 19319, 19321, 29927, 29929, 36479, 36481, 44519, 44521
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OFFSET
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1,1
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COMMENTS
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The sum of reciprocals converges and (1/2) + (1/4) + (1/7) + (1/9) + (1/9) + (1/11) + (1/23) +... = 1.3569053... (constant).
Are there infinitely many pairs?
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LINKS
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MATHEMATICA
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Select[Join @@ Map[{{# - 2, #}, {#, # + 2}} &, Prime@ Range[10^4]], MemberQ[Sqrt@ #, _?(And[PrimeQ@ #] &)] &] // Flatten (* Michael De Vlieger, Jun 09 2017 *)
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PROG
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(PARI) {
forprime(n=2, 300,
if(isprime(n^2-2), print1(n^2-2, ", "n^2", "));
if(isprime(n^2+2), print1(n^2, ", "n^2+2", "))
)
}
(PARI) list(lim)=my(v=List(), t); forprime(p=2, sqrtint(2+lim\1), t=p^2; if(isprime(t-2), listput(v, t-2); listput(v, t)); if(isprime(t+2), listput(v, t); listput(v, t+2))); select(k->k<=lim, Vec(v)) \\ Charles R Greathouse IV, Jun 09 2017
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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