A159345 a(n) is the number of digits in the decimal expansion of Pi needed to contain a repeated n-digit substring.

3, 22, 63, 135, 555, 1301, 4607, 15441, 33852, 240488, 694409, 857993, 5563724, 9289707, 28048931, 129440103, 262527982, 1982424660, 8858170624, 17601613331

Offset: 1

Author

Peter de Rivaz, Oct 15 2011

Keywords

• base
• nonn
• hard

Examples

			We need 3 digits (141) to find the first digit to repeat (the repeated digit is 1).
We need 22 digits (1415926535897932384626) to find the first 2 digit repeat (the repeated 2-digit substring is 26).
		

Links

• Dave Andersen, The Pi-Search Page.
• David H. Bailey, The computation of to 29,360,000 decimal digits using Borweins' quartically convergent algorithm, Mathematics of Computation, 50(1988), 283-296.

Crossrefs

Cf. A000796 (Pi), A197123 (the repeated substring).

Extensions

a(20) from Jeff Sponaugle, Aug 13 2024