A249407 Numbers not in A249406.

2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70

Offset

1,1

Comments

Primes are a subsequence, but semiprimes (cf. A001358) are not: first missing: A249406(1)=6=2*3, A249406(732)=2196323=1481*1483, A249406(1263)=6502499=2549*2551, A249406(1472)=8820899=2969*2971, A249406(1756)=12531599=3539*3541, ... ;

see A249411 for numbers of the form m*(m+1).

Links

Table of n, a(n) for n=1..66.

Prog

(Haskell)
import Data.List ((\\))
a249407 n = a249407_list !! (n-1)
a249407_list = f [2..] where
   f ws@(u:v:_) = u : v : f (ws \\ [u, v, u * v])

Crossrefs

Cf. A249406 (complement), A000040 (subsequence), A001358.

Sequence in context: A080907 A127161 A129657 * A360305 A103679 A029916

Adjacent sequences: A249404 A249405 A249406 * A249408 A249409 A249410

Keyword

nonn

Author

Reinhard Zumkeller, Oct 31 2014

Status

approved