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A135615 a(n) = number of positive divisors of (n+1) that are each the average of a positive divisor of n and a positive divisor of (n+2). 1
2, 2, 3, 2, 3, 2, 4, 3, 4, 2, 3, 2, 4, 4, 4, 2, 3, 2, 5, 3, 4, 2, 4, 3, 4, 3, 4, 2, 3, 2, 4, 3, 4, 4, 5, 2, 4, 3, 4, 2, 3, 2, 4, 3, 4, 2, 4, 3, 5, 3, 4, 2, 5, 4, 6, 3, 4, 2, 3, 2, 4, 4, 6, 4, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..2500

FORMULA

a(n) <= A000005(n+1). - Michel Marcus, Oct 23 2016

EXAMPLE

The divisors of 5 are (1,5). The divisors of 6 are (1,2,3,6). And the divisors of 7 are (1,7). Looking at the divisors of 6, 1 is the average of 1 (from the divisors of 5) and 1 (from the divisors of 7). 3 is the average of 5 (from the divisors of 5) and 1 (from the divisors of 7). And 6 is the average of 5 (from the divisors of 5) and 7 (from the divisors of 7). 2 is not the average of any divisor of 5 and any divisor of 7. There are 3 divisors of 6 that are such averages, so a(5) = 3.

MATHEMATICA

Table[Length[Intersection[Divisors[n + 1], Mean /@ Flatten[Outer[List, Divisors[n], Divisors[n + 2]], 1]]], {n, 1, 65}]  (* Brad Chalfan (brad(AT)chalfan.net), Aug 31 2010 *)

CROSSREFS

Cf. A000005 (number of divisors).

Sequence in context: A326082 A067554 A135981 * A166469 A080226 A060741

Adjacent sequences:  A135612 A135613 A135614 * A135616 A135617 A135618

KEYWORD

nonn

AUTHOR

Leroy Quet, Feb 28 2008

EXTENSIONS

More terms from Brad Chalfan (brad(AT)chalfan.net), Aug 31 2010

STATUS

approved

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Last modified July 28 17:15 EDT 2021. Contains 346335 sequences. (Running on oeis4.)