A307001 Odd numbers > 1 not of the form (3n*k - n - k + 1)/2 where n and k are odd numbers > 1.

3, 5, 7, 9, 13, 15, 17, 21, 23, 25, 29, 31, 37, 39, 41, 45, 49, 53, 55, 57, 63, 65, 69, 71, 73, 77, 79, 81, 85, 93, 95, 97, 101, 105, 109, 111, 119, 121, 125, 129, 133, 135, 137, 141, 143, 149, 151, 153, 157, 161, 169, 175, 177, 181, 183, 185, 189, 193, 197

Offset: 1

Author

David Lovler, Mar 19 2019

Keywords

• nonn
• easy

Comments

Terms are the odd numbers > 1 not appearing in array A322744 with its first row and column omitted.

They are the odd numbers in A307002. - David Lovler, Jan 17 2022

Crossrefs

Cf. A322744, A307002.

Programs

Mathematica

Select[2 Range[100]-1, FindInstance[# == 1 + 2*n + k (2 + 6 n) && n>0 && k>0, {n,k}, Integers] === {} &] (* Giovanni Resta, May 06 2019 *)

PARI

isok(n) = {my(kj, tij); if (n % 2, forstep (i=3, oo, 2, kj = 0; forstep (j=3, i, 2, tij = (3*i*j - i - j +1)/2; if (tij == n, return (0)); if (tij > n, kj = j; break);); if ((kj == 3) && (tij > n), break);); return (n>1));} \\ Michel Marcus, Apr 24 2019 and Jan 25 2022

Extensions

Definition amended by David Lovler, Jan 25 2022