A087146 - OEIS

A087146

Numbers k such that k! + (k+1)! - 1 is prime.

1, 2, 3, 5, 9, 13, 14, 17, 27, 28, 33, 39, 103, 115, 205, 291, 1431, 1532, 1710, 1937, 3901, 3981, 4682, 6569, 20266, 20662

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OFFSET

1,2

COMMENTS

291 is in the sequence and also is in the sequence A087147, thus (291!+292!-1,291!+292!+1) is a twin pair of primes. Any additional terms are greater than 1800 with the next prime having more than 5086 digits.

a(27) > 25000. - Robert Price, Jul 12 2015

a(1)-a(26) give certified primes. - Robert Price, Jul 12 2015

REFERENCES

H. Dubner, Factorial and primorial primes, J. Rec. Math., 19(No. 3, 1987)

LINKS

Table of n, a(n) for n=1..26.

EXAMPLE

3 is in the sequence because 3!+4!-1=29 is prime.

MATHEMATICA

v={}; Do[If[PrimeQ[n!+(n+1)!-1], v=Append[v, n]; Print[v]], {n, 1800}]; v

CROSSREFS

Cf. A087147, A051856, A125174 (corresponding primes).

Sequence in context: A108168 A245905 A366482 * A033945 A098142 A270812

Adjacent sequences: A087143 A087144 A087145 * A087147 A087148 A087149

KEYWORD

nonn

AUTHOR

Farideh Firoozbakht, Aug 19 2003

EXTENSIONS

One more term from Ryan Propper, Aug 13 2005

a(21)-a(26) from Robert Price, Jul 12 2015

STATUS

approved