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

1,8

Links

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

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).

Mathematica

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

Prog

(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))

Crossrefs

Cf. A093347, A093348

Sequence in context: A291423 A276792 A188943 * A309641 A020789 A153857

Adjacent sequences: A093346 A093347 A093348 * A093350 A093351 A093352

Keyword

nonn

Author

Benoit Cloitre, Apr 26 2004

Status

approved