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A306190
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a(n) = p^2 - p - 1 where p = prime(n), the n-th prime.
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2
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1, 5, 19, 41, 109, 155, 271, 341, 505, 811, 929, 1331, 1639, 1805, 2161, 2755, 3421, 3659, 4421, 4969, 5255, 6161, 6805, 7831, 9311, 10099, 10505, 11341, 11771, 12655, 16001, 17029, 18631, 19181, 22051, 22649, 24491, 26405, 27721, 29755, 31861, 32579, 36289
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OFFSET
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1,2
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COMMENTS
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Terms are divisible by 5 iff p is of the form 10*m + 3 (A030431).
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LINKS
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FORMULA
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Product_{n>=1} (1 + 1/a(n)) = A065488.
Product_{n>=2} (1 - 1/a(n)) = A065479. (End)
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EXAMPLE
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a(3) = 19 because 5^2 - 5 - 1 = 19.
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MAPLE
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map(p -> p^2-p-1, [seq(ithprime(i), i=1..100)]); # Robert Israel, Mar 11 2019
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MATHEMATICA
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Table[Prime[n]^2-Prime[n]-1, {n, 1, 100}] (* Jinyuan Wang, Feb 02 2019 *)
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PROG
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(PARI) a(n) = {p=prime(n); p^2-p-1; } \\ Jinyuan Wang, Feb 02 2019
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CROSSREFS
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A039914 is an essentially identical sequence.
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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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