A068632 a(1) = 2; a(n+1) = smallest composite number not in the sequence such that the sum of all the terms is prime.

2, 9, 6, 12, 8, 4, 18, 14, 10, 20, 24, 22, 30, 32, 16, 36, 44, 40, 26, 28, 38, 48, 34, 42, 50, 46, 60, 54, 56, 52, 66, 62, 78, 64, 72, 68, 70, 86, 76, 74, 96, 84, 90, 82, 80, 58, 92, 88, 104, 102, 106, 98, 100, 110, 112, 120, 132, 108, 140, 94, 116, 114, 124, 126, 128, 136

Offset

0,1

Links

Table of n, a(n) for n=0..65.

Example

a(3) = 6 not 4 as 2 + 9 + 6 = 17 is prime, while 2+9 +4 = 15 is composite.

Maple

a[1] := 2:for i from 2 to 120 do j := 2:while(true)do j := j+1: if((not isprime(j)) and (not (j=a[i-1]))) then bo := true: for h from 1 to i-1 do if(a[h]=j) then bo := false end if:end do: if(isprime(sum(a[k], k=1..i-1)+j) and bo=true) then a[i] := j:break:end if:end if:end do:end do:seq(a[k], k=1..120);

Crossrefs

Cf. A068631.

Sequence in context: A021341 A011247 A201736 * A320037 A122664 A318649

Adjacent sequences: A068629 A068630 A068631 * A068633 A068634 A068635

Keyword

easy,nonn

Author

Amarnath Murthy, Feb 26 2002

Extensions

Corrected and extended by Sascha Kurz, Mar 26 2002

Status

approved