OFFSET
1,1
COMMENTS
Number of ways of writing 10^n as the sum of two odd primes, when the order does not matter.
LINKS
Ivars Peterson's MathTrek, Goldbach's Prime Pairs
Science News Online, Goldbach's Prime Pairs, week of Aug. 19, 2000; Vol. 158, No. 8.
FORMULA
a(n) = A061358(10^n).
EXAMPLE
a(1)=2 because 10 = 3+7 = 5+5;
a(2)=6 because 100 = 3+97 = 11+89 = 17+83 = 29+71 = 41+59 = 47+53; ...
MATHEMATICA
NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; f[n_] := Block[{c = 0, lmt = n/2, p = 3}, While[p <= lmt, If[ PrimeQ[n - p], c++ ]; p = NextPrim@p]; c]; Array[f, 10] (* Robert G. Wilson v, Nov 01 2006 *)
a[n]:=Length[Select[n - Prime[Range[PrimePi[n/2]]], PrimeQ]]; Table[a[n], {n, 10^3, 10^3}] (* Luciano Ancora, Mar 16 2015 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert G. Wilson v, Dec 01 2001
EXTENSIONS
a(9) from Zak Seidov Nov 01 2006
a(10) from R. J. Mathar and David W. Wilson, Nov 02 2006
a(11) from David W. Wilson and Russ Cox, Nov 03 2006
a(12) from Russ Cox, Nov 04 2006
a(13) from Donovan Johnson, Nov 16 2009
a(14) from Huang Yuanbing (bailuzhou(AT)163.com), Dec 24 2009
STATUS
approved