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A078402
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Numbers n such that n^2 + 5 is prime.
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13
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0, 6, 12, 36, 48, 72, 78, 96, 114, 126, 162, 168, 198, 204, 246, 258, 294, 336, 342, 372, 414, 432, 456, 462, 492, 504, 516, 534, 552, 576, 588, 594, 624, 666, 714, 726, 756, 768, 786, 792, 798, 804, 834, 852, 876, 888, 918, 954, 996
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| The sum of the reciprocals of the primes generated from these indices converges to 0.2332142.. The sum of the reciprocals of these indices cannot be computed.
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LINKS
| Eric Weisstein's World of Mathematics, Near-Square Prime
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MATHEMATICA
| lst={}; Do[If[PrimeQ[n^2+5], Print[n]; AppendTo[lst, n]], {n, 10^5}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Aug 21 2008]
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PROG
| (PARI) \Indices of primes of the form n^2 + 5 and the sum of the reciprocals. nsqpm(n) = {sr=0; forstep(x=0, n, 2, y = x*x+5; if(isprime(y), print1(x" "); sr+=1.0/y; ); ); print(); print(sr); }
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CROSSREFS
| For the primes see A056905(n).
a(n) = 6 * A056906(n)
Sequence in context: A192029 A166636 A167338 * A127845 A096932 A176681
Adjacent sequences: A078399 A078400 A078401 * A078403 A078404 A078405
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KEYWORD
| easy,nonn
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AUTHOR
| Cino Hilliard (hillcino368(AT)gmail.com), Dec 26 2002
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EXTENSIONS
| Offset corrected by Arkadiusz Wesolowski, Aug 09 2011
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