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Search: id:A130096
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| A130096 |
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Primes prime(n) such that both of the numbers (prime(n+1)^2-prime(n)^2)/2 - 1 and (prime(n+1)^2-prime(n)^2)/2 + 1 are not primes. |
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| 31, 47, 59, 71, 79, 83, 101, 107, 113, 127, 131, 149, 151, 157, 173, 193, 211, 223, 229, 233, 271, 311, 317, 337, 347, 349, 373, 383, 389, 401, 439, 457, 461, 467, 487, 491, 509, 521, 523, 541, 563, 569, 571, 593, 647, 653, 661, 683, 709, 727, 733, 743, 773
(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)=31 because (37^2 - 31^2)/2 - 1 = 203 and (37^2 - 31^2)/2 + 1 = 205 (203, 205 are not primes),
a(2)=47 because (53^2 - 47^2)/2 - 1 = 299 and (53^2 - 47^2)/2 + 1 = 301 (299, 301 are not primes),
a(3)=59 because (61^2 - 59^2)/2 - 1 = 119 and (61^2 - 59^2)/2 + 1 = 121 (119, 121 are not primes), ...
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MAPLE
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ts_p3_21:=proc(n) local a, b, i, ans; ans := [ ]: for i from 2 to n do a := (ithprime(i+1)^(2)-ithprime(i)^(2))/2-1: b := (ithprime(i+1)^(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_p3_21(500);
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CROSSREFS
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Cf. A130761.
Sequence in context: A046047 A014313 A095318 this_sequence A075586 A033221 A127576
Adjacent sequences: A130093 A130094 A130095 this_sequence A130097 A130098 A130099
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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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