A073925 Powers of 2 rearranged such that every partial sum (n>1) is composite.

1, 8, 16, 2, 64, 4, 256, 1024, 32, 128, 512, 2048, 8192, 4096, 16384, 32768, 131072, 65536, 2097152, 262144, 524288, 1048576, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 2147483648, 1073741824

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..3319

Example

a(2)=8 because 1+2=3, 1+4=5 are primes and 1+8=9 is composite.

Maple

N:= 100: # for terms before the first > 2^N
Cands:= [seq(2^i, i=0..N)]:
Res:= NULL: s:= 0: nC:= N+1:
found:= true;
while found do
  found:= false;
  for i from 1 to nC do
    if not isprime(s+Cands[i]) then
      Res:= Res, Cands[i];
      s:= s + Cands[i];
      Cands:= subsop(i=NULL, Cands);
      nC:= nC-1;
      found:= true;
      break
    fi
  od
od:
Res; # Robert Israel, Apr 05 2020

Crossrefs

Cf. A073923, A073924.

Sequence in context: A061746 A028585 A073926 * A053321 A335772 A299214

Adjacent sequences: A073922 A073923 A073924 * A073926 A073927 A073928

Keyword

nonn

Author

Amarnath Murthy, Aug 19 2002

Extensions

More terms from Sascha Kurz, Feb 01 2003

Status

approved