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Odd numbers not of the form 2*n*k - n - k + 1 where n and k are odd numbers > 1.
3

%I #24 Jan 10 2021 22:24:08

%S 1,3,5,7,9,11,15,17,19,21,25,27,29,31,35,37,39,45,47,49,51,55,57,61,

%T 65,67,69,71,75,79,81,87,89,91,97,99,101,105,107,109,115,117,119,121,

%U 125,127,129,135,139,141,147,151,155,157,159,161,165,169

%N Odd numbers not of the form 2*n*k - n - k + 1 where n and k are odd numbers > 1.

%C Terms are the odd numbers not appearing in array A327259 with its first row and column omitted.

%H Robert Israel, <a href="/A327260/b327260.txt">Table of n, a(n) for n = 1..10000</a>

%p N:= 201: # for terms <= N

%p f:= (n,k) -> 2*n*k-n-k+1:

%p S:= {seq(i,i=1..N,2)} minus {seq(seq(f(n,k),k=3..min(N,(N+n-1)/(2*n-1)),2),n=3..(N+2)/5,2)}:

%p sort(convert(S,list)); # _Robert Israel_, Sep 09 2020

%t Select[2 Range[100]-1, FindInstance[# == 1 + 2*n + k (2 + 8 n) && n>0 && k>0, {n, k}, Integers] === {} &] (* _David Lovler_, Dec 28 2020 *)

%Y Cf. A307001, A327259, A327261.

%K nonn

%O 1,2

%A _David Lovler_, Aug 27 2019

%E Corrected by _Robert Israel_, Sep 09 2020