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Search: id:A085382
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| A085382 |
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Sum of prime p and largest prime divisor of p-1. |
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+0
1
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| 7, 10, 16, 16, 19, 22, 34, 36, 36, 40, 46, 50, 70, 66, 88, 66, 78, 78, 76, 92, 124, 100, 100, 106, 120, 160, 112, 120, 134, 144, 154, 162, 186, 156, 170, 166, 250, 216, 268, 186, 210, 196, 204, 210, 218, 260, 340, 248, 262, 256, 246, 256, 259, 394, 336, 276, 300
(list; graph; listen)
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OFFSET
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5,1
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COMMENT
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There are few primes in this sequence. They the upper member of twin prime pairs of the form 2^x+1,2^x+3. since we are subtracting 1 from p this is only way a largest even prime divisor can occur namely 2 to add to a prime to get a prime which if it too is prime it will be a twin prime. The next one after 7,19 shown is 2^16+3 = 65539.
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PROGRAM
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(PARI) cminuspm2(n) = \ prime + maxprime of prime-1 { forprime(x=5, n, forstep(p=x, 2, -1, if(isprime(p) & (x-1)%p==0, print1(x+p, ", "); break); ) ) }
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CROSSREFS
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Sequence in context: A120136 A020743 A088350 this_sequence A083390 A033817 A098748
Adjacent sequences: A085379 A085380 A085381 this_sequence A085383 A085384 A085385
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Aug 12 2003
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