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Search: id:A130098
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| A130098 |
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Primes prime(n) such that both of the numbers (prime(n+2)^2-prime(n)^2)/2 - 1 and (prime(n+2)^2-prime(n)^2)/2 + 1 are not primes. |
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1
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| 17, 23, 47, 73, 89, 101, 103, 109, 113, 131, 137, 151, 163, 167, 173, 193, 199, 211, 223, 233, 241, 257, 269, 271, 277, 281, 311, 313, 317, 331, 337, 359, 367, 379, 383, 389, 397, 401, 409, 421, 431, 433, 449, 457, 461, 487, 491, 503, 509, 521, 547, 557, 563
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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a(1)=17 because (23^2 - 17^2)/2 - 1 = 119 and (23^2 - 17^2)/2 + 1 = 121 (119, 121 are not primes),
a(2)=23 because (31^2 - 23^2)/2 - 1 = 215 and (31^2 - 23^2)/2 + 1 = 217 (215, 217 are not primes),
a(3)=47 because (59^2 - 47^2)/2 - 1 = 635 and (59^2 - 47^2)/2 + 1 = 637 (635, 637 are not primes), ...
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MAPLE
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ts_p2_21:=proc(n) local a, b, i, ans; ans := [ ]: for i from 2 to n do a := (ithprime(i+2)^(2)-ithprime(i)^(2))/2-1: b := (ithprime(i+2)^(2)-ithprime(i)^(2))/2+1: if not (isprime(a)=true or isprime(b)=true) then ans := [ op(ans), ithprime(i) ]: fi od; RETURN(ans) end: ts_p2_21(500);
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CROSSREFS
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Cf. A130761.
Sequence in context: A086532 A159044 A126329 this_sequence A046123 A152292 A039319
Adjacent sequences: A130095 A130096 A130097 this_sequence A130099 A130100 A130101
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KEYWORD
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nonn
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AUTHOR
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Jani Melik (jani_melik(AT)hotmail.com), Aug 01 2007
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