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Search: id:A078699
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| A078699 |
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Primes p such that p^2-1 is a triangular number. |
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+0
1
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| 2, 11, 23, 373, 12671, 901273, 19472752251611, 53072032161200090602953513048447623, 5027153581127740201460650182713355379768873, 11604855412241025458500993236724193227031777965785837784548351709747881343573
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Equivalently, primes in A006452.
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MATHEMATICA
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a[n_] := a[n]=If[n<4, {1, 2, 4, 11}[[n+1]], 6a[n-2]-a[n-4]]; Select[a/@Range[200], ProvablePrimeQ] (* First do <<NumberTheory`PrimeQ` *)
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PROGRAM
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(PARI) default(primelimit, 10^7) istri(n) = t=floor(sqrt(2*n)); if(2*n==t*(t+1), 1, 0) forprime(p=2, 5*10^6, if(istri(p^2-1), print1(p" ")))
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CROSSREFS
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Cf. A000217, A006452.
Sequence in context: A141423 A106974 A115374 this_sequence A042347 A041803 A009189
Adjacent sequences: A078696 A078697 A078698 this_sequence A078700 A078701 A078702
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KEYWORD
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nonn
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Dec 18 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Dec 19 2002
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