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A175462 Number of divisors of integers of the form 5 + 8n. 2
2, 2, 4, 2, 2, 6, 2, 2, 4, 4, 4, 4, 2, 2, 6, 4, 4, 4, 2, 2, 8, 2, 2, 8, 2, 4, 4, 4, 2, 4, 6, 4, 6, 2, 2, 8, 2, 4, 4, 2, 6, 6, 4, 2, 8, 4, 2, 4, 2, 2, 10, 4, 2, 8, 4, 4, 4, 2, 4, 6, 4, 4, 4, 2, 4, 12, 4, 2, 6, 2, 4, 4, 4, 4, 4, 6, 2, 8, 4, 6, 8, 2, 2, 4, 2, 4, 12, 2, 2, 4, 6, 2, 8, 4, 2, 12, 2, 4, 4, 2, 8, 4, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
All terms are even.
LINKS
FORMULA
a(n) = d(5 + 8*n).
a(n) = A000005(A004770(n)).
Sum_{k=1..n} a(k) ~ (n/2) * (log(n) + 2*gamma - 1 + 5*log(2)), where gamma is Euler's constant (A001620). - Amiram Eldar, Jan 14 2024
MAPLE
map(numtheory:-tau, [seq(i, i=5..1000, 8)]); # Robert Israel, Mar 20 2020
MATHEMATICA
Table[DivisorSigma[0, 8*n + 5], {n, 0, 100}] (* Amiram Eldar, Jan 14 2024 *)
PROG
(PARI) a(n) = numdiv(5+8*n); \\ Michel Marcus, Oct 15 2013
CROSSREFS
Cf. A004770 (Numbers of form 8n + 5), A007521 (Primes of form 8n + 5). A000005 (d(n) : number of divisors of n), A001620.
Sequence in context: A261891 A321320 A366808 * A133946 A286250 A278244
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, May 23 2010
STATUS
approved

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)