A338792 a(n) is the least number k such that 1/prime(k) has repeating decimal expansion of period n.

1, 2, 5, 12, 26, 13, 4, 52, 21, 28693, 1128, 2431, 1221, 16, 71954, 11, 7, 153888, 8, 27417323062119920, 496, 14, 9, 223378173194137397198, 5760923, 2403, 149, 134, 10, 452, 47, 406, 71, 19, 27, 20, 37607875619, 150886, 22544062111497849

Offset: 0

Author

Ilya Gutkovskiy, Nov 09 2020

Keywords

• nonn
• base

Examples

			1/prime(1)  = 1/2  = 0.5 (finite decimal expansion).
1/prime(2)  = 1/3  = 0.3(3)... (period 1).
1/prime(5)  = 1/11 = 0.09(09)... (period 2).
1/prime(12) = 1/37 = 0.027(027)... (period 3).
		

Links

• Index entries for sequences related to decimal expansion of 1/n

Crossrefs

Cf. A000720, A002371, A003060, A007138.

Formula

a(0) = 1; a(n) = A000720(A007138(n)).

Extensions

a(19)-a(38) from Daniel Suteu, Nov 09 2020 [using data from A007138 and A234317]