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A131089
a(n) = Sum_{d|n} (2 - mu(d)).
1
1, 4, 4, 6, 4, 8, 4, 8, 6, 8, 4, 12, 4, 8, 8, 10, 4, 12, 4, 12, 8, 8, 4, 16, 6, 8, 8, 12, 4, 16, 4, 12, 8, 8, 8, 18, 4, 8, 8, 16, 4, 16, 4, 12, 12, 8, 4, 20, 6, 12, 8, 12, 4, 16, 8, 16, 8, 8, 4, 24, 4, 8, 12, 14, 8, 16, 4, 12, 8, 16, 4, 24, 4, 8, 12, 12, 8, 16
OFFSET
1,2
COMMENTS
Apart from the first term the same as A062011. - Andrew Howroyd, Aug 09 2018
FORMULA
a(n) = 2*tau(n) = A062011(n) for n > 1. - Andrew Howroyd, Aug 09 2018
Inverse Moebius transform of A228483.
EXAMPLE
a(4) = 6 = (2 + 3 + 0 + 1), row 4 of A131088.
MATHEMATICA
Join[{1}, Table[2 DivisorSigma[0, n], {n, 100}]] (* Vincenzo Librandi, Aug 10 2018 *)
PROG
(PARI) a(n)={2*numdiv(n) - (n==1)} \\ Andrew Howroyd, Aug 09 2018
(Magma) [1] cat [2*NumberOfDivisors(n) : n in [2..100] ]; // Vincenzo Librandi, Aug 10 2018
CROSSREFS
Row sums of triangle A131088.
Sequence in context: A077553 A010659 A255014 * A256486 A204068 A066560
KEYWORD
nonn
AUTHOR
Gary W. Adamson, Jun 14 2007
EXTENSIONS
Name changed and terms a(10) and beyond from Andrew Howroyd, Aug 09 2018
STATUS
approved