OFFSET

1,10

COMMENTS

Except for the initial terms, the same sequence as A210469.

LINKS

J. Stauduhar, Table of n, a(n) for n = 1..10000

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

KEYWORD

nonn

AUTHOR

J. Stauduhar, Apr 16 2013

STATUS

approved