A093349 A 7-fractal "castle" starting with 0.

0, 1, 0, 1, 0, 1, 0, 7, 6, 7, 6, 7, 6, 7, 0, 1, 0, 1, 0, 1, 0, 7, 6, 7, 6, 7, 6, 7, 0, 1, 0, 1, 0, 1, 0, 7, 6, 7, 6, 7, 6, 7, 0, 1, 0, 1, 0, 1, 0, 49, 48, 49, 48, 49, 48, 49, 42, 43, 42, 43, 42, 43, 42, 49, 48, 49, 48, 49, 48, 49, 42, 43, 42, 43, 42, 43, 42, 49, 48, 49, 48, 49, 48, 49, 42, 43

Offset: 1

Author

Benoit Cloitre, Apr 26 2004

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A093347, A093348

Programs

Mathematica

a[n_] := Sum[(-1)^(i+1) * 7^IntegerExponent[i, 7], {i, 1, n-1}]; Array[a, 100] (* Amiram Eldar, Jun 17 2022 *)

PARI

a(n)=if(n<2,0,7^floor(log(n-1)/log(7))-a(n-7^floor(log(n-1)/log(7))))

PARI

a(n)=-sum(i=1,n-1,(-1)^i*7^valuation(i,7))

Formula

a(1) = 0 then a(n) = w(n) - a(n-w(n)) where w(n) = 7^floor(log(n-1)/log(7)).

a(n) = Sum_{i=1..n-1} (-1)^(i-1)*7^valuation(i, 7).