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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A258713 A001172(n)/2: Least k such that 2k is a sum of two odd primes in exactly n ways. 2

%I

%S 0,3,5,11,17,24,30,39,42,45,57,72,60,84,90,117,123,144,120,105,162,

%T 150,180,237,165,264,288,195,231,240,210,285,255,336,396,378,438,357,

%U 399,345,519,315,504,465,390,480,435,462,450,567,717,420,495,651

%N A001172(n)/2: Least k such that 2k is a sum of two odd primes in exactly n ways.

%C Up to a(14) also indices of records in A002375, number of ways to write 2n as sum of two odd primes. - _M. F. Hasler_, Aug 21 2017

%H Robert Israel, <a href="/A258713/b258713.txt">Table of n, a(n) for n = 0..845</a>

%p g:= add(x^ithprime(i),i=2..1000):

%p G:= series((g^2+add(x^(2*ithprime(i)),i=2..1000))/2,x,ithprime(1001)+3):

%p A[0]:= 0:

%p for k from 1 to (ithprime(1001)+1)/2 do

%p m:= coeff(G,x,2*k);

%p if not assigned(A[m]) then A[m]:= k fi;

%p od:

%p for m from 1 while assigned(A[m]) do od:

%p seq(A[i],i=0..m-1); # _Robert Israel_, Aug 21 2017

%t With[{s = Array[Count[Select[IntegerPartitions[2 #, 2], Length@ # == 2 &], p_ /; AllTrue[p, And[PrimeQ@ #, OddQ@ #] &]] &, 10^3]}, Table[FirstPosition[s, n][[1]] /. 1 -> 0, {n, 0, 53}]] (* _Michael De Vlieger_, Aug 21 2017 *)

%Y Cf. A001172.

%Y Cf. A002375, A002372, A045917.

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Jun 14 2015

%E Edited by _M. F. Hasler_, Aug 21 2017

%E Edited by _Robert Israel_, Aug 21 2017

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 September 21 22:00 EDT 2019. Contains 327283 sequences. (Running on oeis4.)