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Values of repunits with odd length L in base (L+3)/2 representation.
1

%I #3 Mar 30 2012 18:50:57

%S 1,13,341,19531,2015539,329554457,78536544841,25736391511831,

%T 11111111111111111,6115909044841454629,4182283628124518315101,

%U 3479492117784426363920483,3461445831219105624193478971

%N Values of repunits with odd length L in base (L+3)/2 representation.

%C Central terms of the triangle in A125118: a(n)=A125118(2*n-1,n).

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Repunit.html">Repunit</a>

%F a(n) = Sum((n+1)^k: 0<=k<=2*(n-1)).

%e a(4) = [1111111]_5 = (((((5+1)*5+1)*5+1)*5+1)*5+1)*5+1 = 19531.

%K nonn,base

%O 1,2

%A _Reinhard Zumkeller_, Nov 21 2006