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A361799
Numbers which cannot be expressed as i^2 + j*k with i >= j >= k >= 0.
0
3, 7, 14, 21, 23, 43, 47, 62, 75, 119, 134, 138, 167, 215, 318, 398, 566, 1487
OFFSET
1,1
COMMENTS
Is this list infinite?
a(19) > 3.5 * 10^8. - Delbert L. Johnson, May 04 2024
EXAMPLE
14 is a term because there are no solutions to 14 = i^2 + j*k with i >= j >= k >= 0. Specifically 14 = 3^2 + 5*1 is not a solution because 5 > 3.
117 is not a term because 117 = 9^2 + 6*6.
118 is not a term because 118 = 10^2 + 9*2 (also 118 = 10^2 + 6*3).
PROG
(PARI) isok(n)={for(k=sqrtint(n\2), sqrtint(n), my(r=n-k^2); if(r==0, return(0)); fordiv(r, d, if(d<=k && r/d<=k, return(0)))); 1}
select(isok, [1..2000]) \\ Andrew Howroyd, Mar 24 2023
CROSSREFS
Sequence in context: A310273 A310274 A310275 * A310276 A310277 A354957
KEYWORD
nonn,more
AUTHOR
Gordon Hamilton, Mar 24 2023
EXTENSIONS
a(11)-a(18) from Andrew Howroyd, Mar 24 2023
STATUS
approved