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A165317
a(n) = the number of digits in the binary representation of n that each do not precede or follow a similarly valued digit.
2
1, 2, 0, 1, 3, 1, 0, 1, 2, 4, 2, 0, 2, 1, 0, 1, 2, 3, 1, 3, 5, 3, 2, 0, 1, 3, 1, 0, 2, 1, 0, 1, 2, 3, 1, 2, 4, 2, 1, 3, 4, 6, 4, 2, 4, 3, 2, 0, 1, 2, 0, 2, 4, 2, 1, 0, 1, 3, 1, 0, 2, 1, 0, 1, 2, 3, 1, 2, 4, 2, 1, 2, 3, 5, 3, 1, 3, 2, 1, 3, 4, 5, 3, 5, 7, 5, 4, 2, 3, 5, 3, 2, 4, 3, 2, 0, 1, 2, 0, 1, 3, 1, 0, 2, 3
OFFSET
1,2
COMMENTS
A165316(n) + a(n) = the number of digits in the binary representation of n.
Also number of parts equal to 1 in the composition having index n. For the definition of the index of a composition see A298644. For example, a(18) = 3 since the binary form of 18 is (1)00(1)(0) which has 3 runs of length 1 (each placed between parentheses). The command c(n) from the Maple program yields the composition having index n. - Emeric Deutsch, Jan 29 2018
LINKS
EXAMPLE
184 in binary is 10111001. There are exactly three binary digits (the first and last 1's, and the leftmost 0) that are each not adjacent to a similar digit. So a(184) = 3.
MAPLE
Runs := proc (L) local j, r, i, k: j := 1: r[j] := L[1]: for i from 2 to nops(L) do if L[i] = L[i-1] then r[j] := r[j], L[i] else j := j+1: r[j] := L[i] end if end do: [seq([r[k]], k = 1 .. j)] end proc: RunLengths := proc (L) map(nops, Runs(L)) end proc: c := proc (n) ListTools:-Reverse(convert(n, base, 2)): RunLengths(%) end proc: a := proc (n) local ct, j: ct := 0: for j to nops(c(n)) do if c(n)[j] = 1 then ct := ct+1 else end if end do: ct end proc: seq(a(n), n = 1 .. 105); # most of the Maple program is due to W. Edwin Clark. # Emeric Deutsch, Jan 29 2018
PROG
(Python)
def a(n): return ((n^(n<<1))&(n^(n>>1))).bit_count() + ((n&3)==2)
print([a(n) for n in range(1, 106)]) # Michael S. Branicky, May 12 2024
CROSSREFS
KEYWORD
base,nonn,easy
AUTHOR
Leroy Quet, Sep 14 2009
EXTENSIONS
Extended by Ray Chandler, Mar 13 2010
STATUS
approved