login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A065577 Number of Goldbach partitions of 10^n. 9
2, 6, 28, 127, 810, 5402, 38807, 291400, 2274205, 18200488, 149091160, 1243722370, 10533150855, 90350630388 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..14.

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

Cf. A001031.

Cf. A073610, A107318.

Sequence in context: A189238 A226497 A307523 * A227294 A302336 A225877

Adjacent sequences:  A065574 A065575 A065576 * A065578 A065579 A065580

KEYWORD

nonn

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 17 23:21 EDT 2019. Contains 325109 sequences. (Running on oeis4.)