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 A181898 Smallest positive integer which cannot be calculated by an expression containing n binary operators (any of add, subtract, multiply and divide) whose operands are any integer between 1 and 9; parentheses allowed. 8
 10, 19, 92, 417, 851, 4237, 14771, 73237, 298609 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Derek M. Jones, R program for calculating values EXAMPLE a(2)=92 because at least 3 operators are required, e.g., (2*7 + 9)*4. PROG (R) See Jones link. (PARI) first(n)=my(op=[(x, y)->x+y, (x, y)->x-y, (x, y)->y-x, (x, y)->x*y, (x, y)->x/y, (x, y)->y/x], v=vector(n+1), t); v[1]=[1..9]; for(k=2, #v, my(u=[]); for(i=1, (k+1)\2, my(a=v[i], b=v[k-i]); t=Set(concat(apply(f->setbinop(f, a, b), op))); u=concat(u, t)); v[k]=setminus(Set(u), [0])); t=10; for(i=1, #v, while(setsearch(v[i], t), t++); v[i]=t); v \\ Charles R Greathouse IV, Jan 09 2017 CROSSREFS Cf. A181957, A181958, A181959, A181960, A005520, A048183 (see text of comment). Sequence in context: A007811 A255764 A181957 * A219688 A166706 A131495 Adjacent sequences:  A181895 A181896 A181897 * A181899 A181900 A181901 KEYWORD nonn AUTHOR Derek M. Jones, Apr 03 2012 STATUS approved

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Last modified October 15 07:42 EDT 2019. Contains 328026 sequences. (Running on oeis4.)