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A261063 Number of solutions to c(1)*prime(3) + ... + c(2n-1)*prime(2n+1) = -1, where c(i) = +-1 for i > 1, c(1) = 1. 19
0, 0, 0, 1, 6, 8, 40, 67, 373, 1232, 3330, 13656, 47111, 164957, 582042, 1967152, 7129046, 26655235, 94956602, 353789267, 1300061367, 4765080122, 17726643505, 66038899483, 245431428625, 919911458949, 3457983108462, 12974054097333, 49016641868213, 185510228030858 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

There cannot be a solution for an even number of terms on the l.h.s. because all terms are odd but the r.h.s. is odd, too.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..300

EXAMPLE

a(1) = a(2) = 0 because prime(3) and prime(3) +- prime(4) +- prime(5) are different from -1 for any choice of the signs.

a(3) = 0 because the same sums prime(3) +- ... +- prime(7) is also always different from -1 for any choice of the signs.

a(4) = 1 because prime(3) - prime(4) - prime(5) - prime(6) - prime(7) + prime(8) + prime(9) = -1 is the only solution.

MAPLE

s:= proc(n) option remember;

      `if`(n<4, 0, ithprime(n)+s(n-1))

    end:

b:= proc(n, i) option remember; `if`(n>s(i), 0, `if`(i=3, 1,

      b(abs(n-ithprime(i)), i-1)+b(n+ithprime(i), i-1)))

    end:

a:= n-> b(6, 2*n+1):

seq(a(n), n=1..30);  # Alois P. Heinz, Aug 08 2015

MATHEMATICA

s[n_] := s[n] = If[n<4, 0, Prime[n]+s[n-1]]; b[n_, i_] := b[n, i] = If[n > s[i], 0, If[i == 3, 1, b[Abs[n-Prime[i]], i-1] + b[n+Prime[i], i-1]]]; a[n_] := b[6, 2*n+1]; Table[a[n], {n, 1, 30}] (* Jean-Fran├žois Alcover, Nov 11 2015, after Alois P. Heinz *)

PROG

(PARI) A261063(n, rhs=-1, firstprime=3)={rhs-=prime(firstprime); my(p=vector(2*n-2+bittest(rhs, 0), 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 >> 10.

CROSSREFS

Cf. A261061 - A261062 (starting with prime(1) resp. prime(2)), A261044 (starting with prime(4)), A022894 - A022904, A083309, A022920 (r.h.s. = 0, 1 or 2), A261057, A261059, A261060, A261045 (r.h.s. = -2).

Sequence in context: A025627 A038262 A054102 * A000380 A154153 A164640

Adjacent sequences:  A261060 A261061 A261062 * A261064 A261065 A261066

KEYWORD

nonn

AUTHOR

M. F. Hasler, Aug 08 2015

EXTENSIONS

a(15)-a(30) from Alois P. Heinz, Aug 08 2015

STATUS

approved

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Last modified September 21 23:55 EDT 2019. Contains 327286 sequences. (Running on oeis4.)