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A070689
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Numbers k such that k+1 and k^2+1 are primes.
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19
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1, 2, 4, 6, 10, 16, 36, 40, 66, 126, 130, 150, 156, 180, 210, 240, 250, 256, 270, 280, 306, 396, 400, 420, 430, 466, 490, 556, 570, 576, 646, 690, 700, 750, 760, 826, 906, 910, 936, 946, 966, 1060, 1096, 1150, 1276, 1290, 1306, 1320, 1366, 1566, 1570
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OFFSET
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1,2
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COMMENTS
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For any n > 1 in this sequence, (n+1)*(n^2+1) has the same nonzero digits as its prime factors in base n. - Ely Golden, Dec 12 2016
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LINKS
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MATHEMATICA
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Select[ Range[2000], PrimeQ[ # + 1] && PrimeQ[ #^2 + 1] & ]
Select[Prime[Range[250]], PrimeQ[(#-1)^2+1]&]-1 (* Harvey P. Dale, Feb 10 2022 *)
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PROG
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(PARI) list(lim)=my(v=List()); forprime(p=2, lim+1, if(isprime(1+(p-1)^2), listput(v, p-1))); Vec(v) \\ Charles R Greathouse IV, Dec 13 2016
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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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