|
| |
|
|
A337531
|
|
Number of ways that the divisors of 2n can be written as unordered sums of two other prime divisors of 2n (not necessarily distinct).
|
|
0
|
|
|
|
0, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 1, 2, 1, 4, 1, 1, 2, 2, 3, 2, 1, 2, 2, 2, 1, 3, 1, 2, 3, 2, 1, 2, 1, 2, 2, 2, 1, 2, 2, 2, 2, 2, 1, 5, 1, 2, 3, 1, 2, 3, 1, 2, 2, 4, 1, 2, 1, 2, 3, 2, 2, 3, 1, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 4, 2, 2, 2, 2, 2, 2
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,6
|
|
|
LINKS
|
Table of n, a(n) for n=1..96.
|
|
|
FORMULA
|
a(n) = Sum_{d1|(2*n), d2|(2*n), d3|(2*n), d1,d2 prime} [d1 + d2 = d3], where [ ] is the Iverson bracket.
|
|
|
EXAMPLE
|
a(15) = 3; The divisors of 2*15 = 30 are {1,2,3,5,6,10,15,30} and since 2 + 3 = 5, 3 + 3 = 6 and 5 + 5 = 10, a(15) = 3.
|
|
|
CROSSREFS
|
Cf. A175393.
Sequence in context: A036475 A330746 A316555 * A316556 A187279 A076820
Adjacent sequences: A337528 A337529 A337530 * A337532 A337533 A337534
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Wesley Ivan Hurt, Aug 30 2020
|
|
|
STATUS
|
approved
|
| |
|
|
