

A190681


Number of partitions of 10^n into 2 composite relatively prime parts.


0



0, 0, 2, 61, 899, 11219, 126905, 1374229, 14529946, 151426672, 1563147978, 16031036348
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OFFSET

0,3


LINKS

Table of n, a(n) for n=0..11.


EXAMPLE

a(2)=2 because 10^2 = 9 + 91 = 49 + 51, 9 and 91 are composite and coprime, 49 and 51 are composite and coprime.


MATHEMATICA

a[n_] := Module[{cnt=0}, Do[If[!PrimeQ[k]&&!PrimeQ[10^nk]&&GCD[k, 10^nk]==1, cnt++], {k, 3, (1/2)10^n, 2}]; cnt]


PROG

(PARI) a(n) = my(N=10^n, s=0); forstep(k=9, N/2, [2, 2, 4, 2], s += !isprime(k) & !isprime(Nk)); s \\ Charles R Greathouse IV, May 17 2011
(PARI) a(n)=my(N=10^n, s=0, p=7); forprime(q=11, N/2, forstep(k=p+2, q2, 2, s+=k%5&!isprime(Nk)); p=q); s+sum(k=precprime(N/2)+2, N/2, gcd(k, 10)==1&!isprime(Nk)) \\ Charles R Greathouse IV, May 17 2011


CROSSREFS

Cf. A000041, A023022, A000837.
Sequence in context: A299224 A037065 A065589 * A181005 A289644 A094478
Adjacent sequences: A190678 A190679 A190680 * A190682 A190683 A190684


KEYWORD

nonn


AUTHOR

Zak Seidov, May 17 2011


EXTENSIONS

a(9)a(10) from Charles R Greathouse IV, May 18 2011
a(11) from Charles R Greathouse IV, May 20 2011


STATUS

approved



