A022903 - OEIS

%I #21 Jan 29 2024 10:51:25

%S 0,0,0,1,0,0,0,0,0,6,0,9,0,61,0,131,0,486,0,2029,0,5890,0,21127,0,

%T 75979,0,273657,0,1032161,0,3694665,0,12989200,0,48409376,0,174262116,

%U 0,642786775,0,2402713235,0,8918299277,0,32868170524,0,123143998606,0

%N Number of solutions to c(1)*prime(4) + ... + c(n)*prime(n+3) = 0, where c(i) = +-1 for i>1, c(1) = 1.

%H Alois P. Heinz, <a href="/A022903/b022903.txt">Table of n, a(n) for n = 1..500</a>

%F a(2n-1) = 0 for all n >= 1 because an odd number of odd terms on the l.h.s. cannot sum to zero. - _M. F. Hasler_, Aug 08 2015

%F a(n) = [x^7] Product_{k=5..n+3} (x^prime(k) + 1/x^prime(k)). - _Ilya Gutkovskiy_, Jan 28 2024

%e a(10) counts these 6 solutions: {7, -11, -13, -17, -19, -23, 29, -31, 37, 41}, {7, 11, -13, 17, 19, -23, 29, 31, -37, -41}, {7, 11, -13, 17, 19, 23, -29, -31, 37, -41}, {7, 11, 13, -17, -19, 23, 29, 31, -37, -41}, {7, 11, 13, -17, 19, 23, -29, -31, -37, 41}, {7, 11, 13, 17, -19, -23, 29, -31, 37, -41}.

%p A022903 := proc(n)

%p     local a,b,cs,cslen ;

%p     a := 0 ;

%p     for b from 0 to 2^(n-1)-1 do

%p         cs := convert(b,base,2) ;

%p         cslen := nops(cs) ;

%p         if cslen < n-1 then

%p             cs := [op(cs),seq(0,i=1..n-1-cslen)] ;

%p         end if;

%p         if ithprime(4)+add( (-1+2*op(i-4,cs)) *ithprime(i),i=5..n+3) = 0 then

%p             a := a+1 ;

%p         end if;

%p     end do:

%p     a ;

%p end proc:

%p for n from 1 do

%p     print(n,A022903(n)) ;

%p end do: # _R. J. Mathar_, Aug 06 2015

%t {f, s} = {4, 0}; Table[t = Map[Prime[# + f - 1] &, Range[2, z]]; Count[Map[Apply[Plus, #] &, Map[t # &, Tuples[{-1, 1}, Length[t]]]], s - Prime[f]], {z, 22}]

%t (* A022903, a(n) = number of solutions of "sum = s" using Prime(f) to Prime(f+n-1) *)

%t n = 10; t = Map[Prime[# + f - 1] &, Range[n]]; Map[#[[2]] &, Select[Map[{Apply[Plus, #], #} &, Map[t # &, Map[Prepend[#, 1] &, Tuples[{-1, 1}, Length[t] - 1]]]], #[[1]] == s &]]  (* the 6 solutions of using n=10 primes; _Peter J. C. Moses_, Oct 01 2013 *)

%o (PARI) A022903(n, rhs=0, firstprime=4)={rhs-=prime(firstprime); my(p=vector(n-1, i, prime(i+firstprime))); sum(i=1, 2^#p-1, sum(j=1, #p, (-1)^bittest(i, j-1)*p[j])==rhs)} \\ For illustrative purpose, too slow for n >> 20. - M. F. Hasler, Aug 08 2015

%Y Cf. A022894, A022895, ..., A022904, A083309, A022920 (variants with r.h.s. in {0, 1 or 2}, starting with prime(1), prime(2), prime(3) or prime(4)); A261061 - A261063 and A261045 (r.h.s. = -1); A261057, A261059, A261060, A261045(r.h.s. = -2).

%K nonn

%O 1,10

%A _Clark Kimberling_

%E a(23)-a(49) from _Alois P. Heinz_, Aug 06 2015