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A288153
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Plumb pseudoprimes: odd composites that pass Colin Plumb's extended Euler criterion test.
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1
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1729, 1905, 2047, 2465, 3277, 4033, 4681, 8321, 12801, 15841, 16705, 18705, 25761, 29341, 33153, 34945, 41041, 42799, 46657, 49141, 52633, 65281, 74665, 75361, 80581, 85489, 87249, 88357, 90751, 104653, 113201
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OFFSET
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1,1
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COMMENTS
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Suppose n is composite. Then if n = 1 mod 8, it is in the sequence if 2^((n-1)/4) = 1 or -1 mod n; if n = 3 or 5 mod 8, it is in the sequence if 2^((n-1)/2) = -1 mod n; and if n = 3 mod 8, it is in the sequence if 2^((n-1)/2) = 1 mod n.
a(1) = 1729 is the Hardy-Ramanujan number. - Omar E. Pol, Jun 05 2017
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LINKS
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PROG
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(Perl) use Math::Prime::Util ':all'
foroddcomposites { print "$_, " if is_euler_plumb_pseudoprime($_); } 9, 999999;
(PARI) is(n)=if(n<2 || isprime(n) || n%2==0, return(0)); my(n8=n%8, e=n>>((n8==1)+1), t=Mod(2, n)^e); if(t==1, n8==1 || n8==7, if(t==-1, n8==1 || n8==3 || n8==5, 0))
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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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