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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A022904 Number of solutions to c(1)*prime(4) + ... + c(n)*prime(n+3) = 1, where c(i) = +-1 for i>1, c(1) = 1. 20
0, 0, 0, 0, 0, 0, 3, 0, 1, 0, 6, 0, 32, 0, 110, 0, 252, 0, 1139, 0, 3127, 0, 12743, 0, 39767, 0, 156376, 0, 517381, 0, 1870169, 0, 6786580, 0, 25420402, 0, 90815872, 0, 334621081, 0, 1235976769, 0, 4597232973, 0, 17047065235, 0, 63450750049, 0, 238163814619, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,7

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..500

EXAMPLE

a(7) counts these 3 solutions: {7, -11, 13, 17, -19, 23, -29}, {7, 11, -13, -17, 19, 23, -29}, {7, 11, 13, -17, -19, -23, 29}.

MAPLE

A022904 := proc(n)

    local a, b, cs, cslen ;

    a := 0 ;

    for b from 0 to 2^(n-1)-1 do

        cs := convert(b, base, 2) ;

        cslen := nops(cs) ;

        if cslen < n-1 then

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

        end if;

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

            a := a+1 ;

        end if;

    end do:

    a ;

end proc: # R. J. Mathar, Aug 06 2015

MATHEMATICA

{f, s} = {4, 1}; 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}]

(* A022904, a(n) = number of solutions of "sum = s" using Prime(f) to Prime(f+n-1) *)

n = 7; 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 3 solutions of using n=7 primes; Peter J. C. Moses, Oct 01 2013 *)

CROSSREFS

Cf. A022903, A022920.

Sequence in context: A073278 A081658 A187253 * A238341 A242451 A262964

Adjacent sequences:  A022901 A022902 A022903 * A022905 A022906 A022907

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

Corrected and extended by Clark Kimberling, Oct 01 2013

a(23)-a(50) from Alois P. Heinz, Aug 06 2015

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 February 21 01:29 EST 2019. Contains 320364 sequences. (Running on oeis4.)