A249411 -id:A249411 - cp's OEIS frontend

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

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Reinhard Zumkeller, Oct 31 2014

nonn

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).

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

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])

cp's OEIS Frontend

A249407 Numbers not in A249406.

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