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A224710
The number of unordered partitions {a,b} of 2n-1 such that a and b are composite.
2
0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 4, 5, 5, 5, 6, 7, 7, 8, 8, 8, 9, 9, 10, 11, 11, 12, 13, 13, 13, 14, 15, 15, 16, 16, 16, 17, 18, 18, 19, 19, 20, 21, 21, 22, 23, 24, 24, 25, 25, 25, 26, 26, 26, 27, 27, 28, 29, 30, 31, 32, 33, 33, 34, 34, 35, 36, 36
OFFSET
1,10
COMMENTS
Except for the initial terms, the same sequence as A210469.
LINKS
FORMULA
a(n) = n - 2 - primepi(2n-4) for n>1. - Anthony Browne, May 03 2016
a(A104275(n+2) + 1) = n. - Anthony Browne, May 25 2016
EXAMPLE
n=7: 13 has a unique representation as the sum of two composite numbers, namely 13 = 4+9, so a(7)=1.
MATHEMATICA
Table[Length@ Select[IntegerPartitions[2 n - 1, {2}] /. n_Integer /; ! CompositeQ@ n -> Nothing, Length@ # == 2 &], {n, 71}] (* Version 10.2, or *)
Table[If[n == 1, 0, n - 2 - PrimePi[2 n - 4]], {n, 71}] (* Michael De Vlieger, May 03 2016 *)
CROSSREFS
Subsequence of A224708. Cf. A210469.
Sequence in context: A371587 A194251 A029114 * A210469 A073174 A107631
KEYWORD
nonn
AUTHOR
J. Stauduhar, Apr 16 2013
STATUS
approved

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Last modified September 19 21:59 EDT 2024. Contains 376015 sequences. (Running on oeis4.)