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A280708 Lexicographically earliest sequence such that no subsequence sums to a prime. 1
1, 8, 24, 24, 86, 1260, 1890, 14136, 197400, 10467660, 1231572090 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

This sequence is monotonically increasing.

So far, apart from a(4) this sequence is identical to A052349.

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

For n = 4, a(4) = 24 because all subsets have nonprime sums:

           1 +  8 =  9 = 3^2

           1 + 24 = 25 = 5^2

           8 + 24 = 32 = 2^5

          24 + 24 = 48 = 2^4*3

      1 +  8 + 24 = 33 = 3*11

      1 + 24 + 24 = 49 = 7^2

      8 + 24 + 24 = 56 = 2^3*7

  1 + 8 + 24 + 24 = 57 = 3*19

MAPLE

S:= {0}: count:= 0:

x:= 1:

while x < 10^6 do

  if ormap(s -> isprime(s+x), S) then x:= x+1

  else

    count:= count+1;

    A[count]:= x;

    S:= S union map(`+`, S, x);

  fi

od:

seq(A[i], i=1..count); # Robert Israel, Jan 20 2017

MATHEMATICA

t = {1}; c = 1; Print[1]; While[Length[t] < 11, r = Rest[Subsets[t]]; s = Table[Total[r[[i]]], {i, Length[r]}]; While[PrimeQ[c] || Union[PrimeQ[s + c]] != {False}, c++]; Print[c]; AppendTo[t, c]] (* Hans Havermann, Jan 20 2017 *)

CROSSREFS

Cf. A052349.

Sequence in context: A088448 A005878 A128637 * A109272 A052349 A254448

Adjacent sequences:  A280705 A280706 A280707 * A280709 A280710 A280711

KEYWORD

nonn,hard,more

AUTHOR

Peter Kagey, Jan 07 2017

EXTENSIONS

a(9) and a(10) from Dmitry Kamenetsky, Jan 12 2017

a(11) from Hans Havermann, Jan 20 2017

STATUS

approved

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Last modified August 7 06:02 EDT 2020. Contains 336274 sequences. (Running on oeis4.)