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A119556
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Primes in the sequence f(n+1) = f(n)+((-1)^(n+1))*n!, with f(1)=0.
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1
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5, 101, 4421, 1226280710981, 115578717622022981, 32656499591185747972776747396512425885838364422981, 136372385605079432248118270297843987319730859689490659519593045108637838364422981
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OFFSET
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1,1
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COMMENTS
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REFERENCES
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G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 160.
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LINKS
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EXAMPLE
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f(0)=0, f(1) = 0+((-1)^2)*1! = 1, f(2) = 1+((-1)^3)*2! = -1, f(3) = -1+((-1)^4)*3! = 5, which is prime, so 5 is the first term of the sequence.
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MAPLE
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P:=proc(n) local i, j; j:=0; for i from 1 by 1 to n do j:=j+((-1)^(i+1))*i!; if isprime(j) then print(i); fi; od; end: P(100);
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MATHEMATICA
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nxt[{n_, a_}]:={n+1, a+(-1)^(n+1) n!}; Select[NestList[nxt, {1, 0}, 205][[All, 2]], #>0 && PrimeQ[#]&] (* Harvey P. Dale, Sep 10 2018 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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