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 A258070 Nonnegative integers that can be computed using exactly nine 9's and the four basic arithmetic operations {+, -, *, /}. 13
 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The smallest non-computable number here is 195. The largest computable number here is 9^9 = 387420489. LINKS Alois P. Heinz, Table of n, a(n) for n = 1..4769 MAPLE f:= proc(n) f(n):= `if`(n=1, {9}, {seq(seq(seq([x+y, x-y, x*y,       `if`(y=0, [][], x/y)][], y=f(n-j)), x=f(j)), j=1..n-1)})     end: sort([select(z->z>=0 and is(z, integer), f(9))[]])[]; PROG (PARI) A258070(n=9, S=Vec([[n]], n))={for(n=2, n, S[n]=Set(concat(vector(n\2, k, Set(concat([Set(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])} \\ Requires at least 30 MB stack. (Use allocatemem()). A258070() yields this sequence, use optional arg to compute variants. - M. F. Hasler, Nov 26 2018 CROSSREFS Cf. A171826, A171827, A171828, A171829, A258068, A258069, A258071. Cf. A182002, A258097. Sequence in context: A105811 A209662 A272813 * A258071 A266279 A296879 Adjacent sequences:  A258067 A258068 A258069 * A258071 A258072 A258073 KEYWORD nonn,fini,full AUTHOR Alois P. Heinz, May 18 2015 STATUS approved

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Last modified July 23 12:19 EDT 2021. Contains 346259 sequences. (Running on oeis4.)