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A175193
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a(n) is the smallest positive integer such that (the n-th prime)+a(n)! is prime, or -1 if no such prime exists.
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4
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1, 2, 2, 3, 2, 3, 2, 4, 3, 2, 3, 3, 2, 4, 3, 3, 2, 3, 3, 2, 3, 4, 3, 4, 3, 2, 3, 2, 5, 4, 4, 3, 2, 4, 2, 3, 3, 5, 3, 3, 2, 9, 2, 3, 2, 4, 5, 3, 2, 5, 3, 2, 7, 3, 3, 3, 2, 3, 3, 2, 4, 4, 3, 2, 4, 8, 3, 5, 2, 4, 3, 4, 3, 3, 5, 3, 5, 4, 5, 4, 2, 5, 2, 3, 4, 3, 5, 3, 2, 4, 4, 4, 5, 7, 4, 3, 6, 2, 4, 3, 4, 3, 3, 2, 3
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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EXAMPLE
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Records and their indices in a(n):
i n a(n)
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1 1 1
2 2 2
3 4 3
4 8 4
5 29 5
6 42 9
7 233 10
8 254 42
9 4508 49
10 7003 124
11 7385 276
12 60650 311
13 97146 542
(End)
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MATHEMATICA
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Fold[Append[#1, SelectFirst[Range[12], Function[k, PrimeQ[Prime[#2] + k!]]]] &, {1}, Range[2, 105]] (* Michael De Vlieger, Nov 24 2017 *)
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PROG
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(PARI) a(n) = {my(k = 1, p = prime(n)); while (!isprime(p + k!), k++); k; } \\ Michel Marcus, Nov 25 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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EXTENSIONS
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STATUS
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approved
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