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A110412 Sum_{d<n is a divisor of n} tau(n-d). 2
0, 1, 2, 4, 3, 7, 4, 9, 8, 9, 4, 17, 6, 10, 14, 18, 5, 20, 6, 21, 16, 12, 4, 33, 14, 13, 18, 24, 6, 33, 8, 29, 18, 12, 18, 44, 9, 13, 17, 41, 8, 37, 8, 26, 39, 14, 4, 57, 18, 30, 20, 28, 6, 41, 20, 45, 20, 14, 4, 68, 12, 16, 40, 46, 25, 43, 8, 25, 18, 44, 8, 80, 12, 16, 42, 30, 22, 42, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
FORMULA
It appears that a(n) > tau(n) for n >= 4.
EXAMPLE
a(9) = tau(9-1)+tau(9-3) = tau(8)+tau(6) = 4+4 = 8.
MAPLE
with(numtheory): a:=proc(n) local div: div:=divisors(n): sum(tau(n-div[j]), j=1..tau(n)-1): end: seq(a(n), n=2..90); # Emeric Deutsch, Aug 05 2005
MATHEMATICA
f[n_] := Plus @@ (DivisorSigma[0, n - # ] & /@ Most[Divisors[n]]); Table[ f[n], {n, 79}] (* Robert G. Wilson v, Aug 05 2005 *)
PROG
(PARI) a(n) = sumdiv(n, d, if (d<n, numdiv(n-d))); \\ Michel Marcus, Aug 20 2019
CROSSREFS
Cf. A007425.
Sequence in context: A181049 A007203 A354707 * A266285 A258851 A194031
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Jul 31 2005
EXTENSIONS
Edited, corrected and extended by Emeric Deutsch and Robert G. Wilson v, Aug 05 2005
STATUS
approved

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Last modified April 21 00:22 EDT 2024. Contains 371850 sequences. (Running on oeis4.)