OFFSET
1,2
COMMENTS
A117499(a(n)) = 4;
(a(n)-1,a(n)+1) are twin prime pairs for n >= 4.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
EXAMPLE
a(1) = 1: the required 4 subsets of {1-1,1,1+1} are: {2}, {0,2}, {1,2} and {0,1,2}.
MATHEMATICA
Select[Range[170000], Count[Total/@Subsets[{#-1, #, #+1}], _?PrimeQ]==4&] (* Harvey P. Dale, Jul 30 2019 *)
PROG
(Haskell)
a221310 n = a221310_list !! (n-1)
a221310_list = map (+ 1) $ elemIndices 4 a117499_list
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 10 2013
STATUS
approved