A331882 - OEIS

%I #12 Feb 28 2020 23:07:42

%S 1,22,219,1805,25499,168882,3566679,29325629

%N a(n) is the number of digits in the decimal expansion of the fractional part of Pi needed to contain n occurrences of an n-digit substring.

%e a(1) = 1, because we need 1 digit to have the first 1-digit substring ('1') appearing 1 time;

%e a(2) = 22, because we need 22 digits (1415926535897932384626) to have the first 2-digit substring ('26') appearing 2 times;

%e a(3) is 219, because we need 219 digits (1415....933446) to have the first 3-digit substring ('446') appearing 3 times;

%e and so on.

%Y Cf. A000796, A159345, A331881 (the repeated n-digit substrings).

%K nonn,base,hard,more

%O 1,2

%A _Stijn Dierckx_, Jan 30 2020