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A007963 Number of (unordered) ways of writing 2n+1 as a sum of 3 odd primes. 12
0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 6, 7, 6, 8, 7, 9, 10, 10, 10, 11, 12, 12, 14, 16, 14, 16, 16, 16, 18, 20, 20, 20, 21, 21, 21, 27, 24, 25, 28, 27, 28, 33, 29, 32, 35, 34, 30, 37, 36, 34, 42, 38, 36, 46, 42, 42, 50, 46, 47, 53, 50, 45, 56, 54, 46, 62, 53, 48, 64, 59, 55, 68, 61, 59, 68 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

COMMENTS

Ways of writing 2n+1 as p+q+r where p,q,r are odd primes with p <= q <= r.

The two papers of Helfgott appear to provide a proof of the Odd Goldbach Conjecture that every odd number greater than five is the sum of three primes. (The paper is still being reviewed.) - Peter Luschny, May 18 2013; N. J. A. Sloane, May 19 2013

REFERENCES

George E. Andrews, Number Theory (NY, Dover, 1994), page 111.

Ivars Peterson, The Mathematical Tourist (NY, W. H. Freeman, 1998, pages 35-37.

Paulo Ribenboim, "VI, Goldbach's famous conjecture," The New Book of Prime Number Records, 3rd ed. (NY, Springer, 1996), pages 291-299.

LINKS

T. D. Noe, Table of n, a(n) for n = 0..10000

H. A. Helfgott, Minor arcs for Goldbach's problem, arXiv:1205.5252 [math.NT], 2012.

H. A. Helfgott, Major arcs for Goldbach's theorem, arXiv:1305.2897 [math.NT], 2013.

H. A. Helfgott, The ternary Goldbach conjecture is true, arxiv:1312.7748 [math.NT], 2013.

H. A. Helfgott, The ternary Goldbach problem, arXiv:1404.2224 [math.NT], 2014.

F. Smarandache, Only Problems, Not Solutions!.

Index entries for sequences related to Goldbach conjecture

EXAMPLE

a(10) = 4 because 21 = 3+5+13 = 3+7+11 = 5+5+11 = 7+7+7.

MAPLE

A007963 := proc(n)

    local a, i, j, k, p, q, r ;

    a := 0 ;

    for i from 2 do

        p := ithprime(i) ;

        for j from i do

            q := ithprime(j) ;

            for k from j do

                r := ithprime(k) ;

                if p+q+r = 2*n+1 then

                    a := a+1 ;

                elif p+q+r > 2*n+1 then

                    break;

                end if;

            end do:

            if p+2*q > 2*n+1 then

                break;

            end if;

        end do:

        if 3*p > 2*n+1 then

            break;

        end if;

    end do:

    return a;

end proc:

seq(A007963(n), n=0..30) ; # R. J. Mathar, Sep 06 2014

MATHEMATICA

nn = 75; ps = Prime[Range[2, nn + 1]]; c = Flatten[Table[If[i >= j >= k, i + j + k, 0], {i, ps}, {j, ps}, {k, ps}]]; Join[{0, 0, 0, 0}, Transpose[Take[Rest[Sort[Tally[c]]], nn+2]][[2]]] (* T. D. Noe, Apr 08 2014 *)

PROG

(Sage)

def A007963(n):

    c = 0

    for p in Partitions(n, length = 3):

        b = True

        for t in p:

            b = is_prime(t) and t > 2

            if not b: break

        if b : c = c + 1

    return c

[A007963(2*n+1) for n in (0..77)]   # Peter Luschny, May 18 2013

(Perl) use ntheory ":all"; sub a007963 { my($n, $c)=(shift, 0); forpart { $c++ if vecall { is_prime($_) } @_; } $n, {n=>3, amin=>3}; $c; }

say "$_ ", a007963(2*$_+1) for 0..100; # Dana Jacobsen, Mar 19 2017

(PARI) a(n)=my(k=2*n+1, s, t); forprime(p=(k+2)\3, k-6, t=k-p; forprime(q=t\2, min(t-3, p), if(isprime(t-q), s++))); s \\ Charles R Greathouse IV, Mar 20 2017

CROSSREFS

Cf. A068307, A087916, A294294 (lower bound of scatterplot), A294357, A294358 (records).

Sequence in context: A092982 A248868 A030566 * A137222 A077641 A194210

Adjacent sequences:  A007960 A007961 A007962 * A007964 A007965 A007966

KEYWORD

nonn

AUTHOR

R. Muller

EXTENSIONS

Corrected and extended by David W. Wilson

STATUS

approved

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Last modified November 20 10:31 EST 2017. Contains 294963 sequences.