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A265098
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Integers n such that A138523(n) is 1 or a prime.
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0
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OFFSET
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1,2
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COMMENTS
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Inspired by the following triangle for the initial terms:
1! = 1.
1! + 3! = 7.
1! + 3! + 5! = 127.
1! + 3! + 5! + 7! = 5167.
1! + 3! + 5! + 7! + 9! = 368047.
This sequence is finite since 107 divides A138523(n) for all n >= 53. - Amiram Eldar, Apr 20 2017
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LINKS
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EXAMPLE
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a(4) = 4 because 1! + 3! + 5! + 7! = 5167 is prime.
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MATHEMATICA
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Select[Range@ 1000, Or[# == 1, PrimeQ@ #] &@ Sum[(2 k - 1)!, {k, #}] &] (* Michael De Vlieger, Dec 01 2015 *)
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PROG
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(PARI) lista(nn) = { print1(1, ", "); s = 0; for(k=1, nn, s += (2*k-1)!; if(ispseudoprime(s), print1(k, ", ")); ); }
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CROSSREFS
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KEYWORD
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nonn,fini,full
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AUTHOR
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STATUS
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approved
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