OFFSET
1,3
COMMENTS
Every integer can be made if other operators are allowed (i.e., 13 = (5!+5+5)/(5+5)). The sequence is finite: a(68) = 5*5*5*5*5 = 3125 is the last term.
LINKS
Wikipedia, Four Fours
EXAMPLE
Example: a(14) = 14 = (5+5+5)-(5/5).
PROG
(PARI) A171828(n=5, S=Vec([[n]], n))={for(n=2, n, S[n]=Set(concat(vector(n\2, k, concat([concat([[T+U, T-U, U-T, if(U, T/U), if(T, U/T), T*U] | T <- S[n-k]]) | U <- S[k]]))))); select(t->t>=0 && type(t)=="t_INT", S[n])} \\ A171828() yields this sequence, use optional arg to compute variants. - M. F. Hasler, Nov 24 2018
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
Sergio Pimentel, Dec 19 2009
STATUS
approved