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A175548
Binary weight of sigma(n).
6
1, 2, 1, 3, 2, 2, 1, 4, 3, 2, 2, 3, 3, 2, 2, 5, 2, 4, 2, 3, 1, 2, 2, 4, 5, 3, 2, 3, 4, 2, 1, 6, 2, 4, 2, 5, 3, 4, 3, 4, 3, 2, 3, 3, 4, 2, 2, 5, 4, 5, 2, 3, 4, 4, 2, 4, 2, 4, 4, 3, 5, 2, 3, 7, 3, 2, 2, 6, 2, 2, 2, 4, 3, 4, 5, 3, 2, 3, 2, 5, 5, 6, 3, 3, 4, 2, 4, 4, 4, 5, 3, 3, 1, 2, 4, 6, 3, 5, 4, 5, 4, 4, 3, 4, 2
OFFSET
1,2
COMMENTS
The sequence is considered in connection with A175522, A175524, A175526.
a(n)=1 if n is in A046528. - Robert Israel, Nov 07 2017
FORMULA
a(n) = A000120(A000203(n)).
EXAMPLE
a(4) = 3 because the divisors of 4 add up to 7, a number which in binary is written as 3 ones.
MAPLE
seq(convert(convert(numtheory:-sigma(n), base, 2), `+`), n=1..100); # Robert Israel, Nov 07 2017
MATHEMATICA
Table[Plus@@IntegerDigits[DivisorSigma[1, n], 2], {n, 80}] (* Alonso del Arte, Dec 03 2010 *)
PROG
(PARI) a(n) = hammingweight(sigma(n)); \\ Michel Marcus, Feb 08 2016
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Vladimir Shevelev, Dec 03 2010
EXTENSIONS
More terms from Antti Karttunen, Nov 07 2017
STATUS
approved