A196509 Largest palindrome formed by using n single-digit numbers and the operators +, -, * and / where concatenation is not allowed.

9, 11, 343, 747, 6556, 65856, 405504, 4251524, 8847488

Offset: 1

Author

Kausthub Gudipati, Oct 03 2011

Keywords

• nonn
• base
• more

Comments

This puzzle is easily trivial if exponentiation or concatenation is allowed.

Best known results for a(10)..a(15) are 88499488, 846747648, 4095995904, 23613431632, 68899199886, 633498894336.

Erich Friedman solved and proved most of these terms.

Examples

			11 = 9 + 2
343 = 7 * 7 * 7
747 = 9 * (9 * 9 + 2)
6556 = 9 * 9 * 9 * 9 - 5
65856 = 3 * 7 * 7 * 8 * 8 * 8
405504 = 8 * 8 * 8 * 8 * 9 * (9 + 2)
4251524 = 8 * 9 * 9 * 9 * 9 * 9 * 9 - 4
8847488 = 8 * 8 * (5 * 6 * 8 * 8 * 8 * 9 + 2)
		

Links

• Erich Friedman, Problem of the month June 1999

Crossrefs

Cf. A002113.