We construct an explicit totally positive integer $ \alpha_D\in\mathcal O_K^+ $ and prove that $ p_K(\alpha_D) = 8 $ whenever $ K = \mathbb Q(\sqrt D) $ is a real quadratic field satisfying $ \{\xi_D\} < 1/3 $. The set of such radicands $ D $ has positive density. Hence our construction provides an explicit positive density family of real quadratic fields in which the value $ 8 $ occurs. Independently, Zindulka's general theorem implies that the exceptional set $ \mathcal D(8) $ has natural density zero, so $ 8 $ is attained in almost all real quadratic fields. The construction applies uniformly to both congruence classes $ D\equiv 2, 3\pmod 4 $ and $ D\equiv 1\pmod 4 $. We also exhibit the complete list of 8 partitions for several square-free radicands and show that infinitely many fields satisfy the required condition.
Citation: Jing-Jun Yu. Totally positive integers with 8 partitions in real quadratic fields[J]. AIMS Mathematics, 2026, 11(10): 34360-34368. doi: 10.3934/math.20261341
We construct an explicit totally positive integer $ \alpha_D\in\mathcal O_K^+ $ and prove that $ p_K(\alpha_D) = 8 $ whenever $ K = \mathbb Q(\sqrt D) $ is a real quadratic field satisfying $ \{\xi_D\} < 1/3 $. The set of such radicands $ D $ has positive density. Hence our construction provides an explicit positive density family of real quadratic fields in which the value $ 8 $ occurs. Independently, Zindulka's general theorem implies that the exceptional set $ \mathcal D(8) $ has natural density zero, so $ 8 $ is attained in almost all real quadratic fields. The construction applies uniformly to both congruence classes $ D\equiv 2, 3\pmod 4 $ and $ D\equiv 1\pmod 4 $. We also exhibit the complete list of 8 partitions for several square-free radicands and show that infinitely many fields satisfy the required condition.
| [1] |
D. Stern, M. Zindulka, Partitions in real quadratic fields, Math. Nachr., 298 (2025), 548–566. https://doi.org/10.1002/mana.202300480 doi: 10.1002/mana.202300480
|
| [2] | G. E. Andrews, K. Eriksson, Integer partitions, Cambridge University Press, Cambridge, 2004. https://doi.org/10.1017/CBO9781139167239 |
| [3] |
A. Dress, R. Scharlau, Indecomposable totally positive numbers in quadratic orders, J. Number Theory, 14 (1982), 292–306. https://doi.org/10.1016/0022-314X(82)90064-6 doi: 10.1016/0022-314X(82)90064-6
|
| [4] |
M. Zindulka, Totally positive elements with $m$ partitions exist in almost all real quadratic fields, Proc. Edinb. Math. Soc., 69 (2026), 701–734. https://doi.org/10.1017/s0013091525101259 doi: 10.1017/s0013091525101259
|
| [5] | D. A. Cox, Primes of the form $x^2+ny^2$, 2nd edn, Hoboken, NJ, 2013. https://doi.org/10.1090/chel/387 |
| [6] |
T. Estermann, Einige Sätze über quadratfeie Zahlen, Math. Ann., 105 (1931), 653–662. https://doi.org/10.1007/BF01455836 doi: 10.1007/BF01455836
|
| [7] |
G. Ricci, Ricerche aritmetiche sui polinomi, Rend. Circ. Mat. Palermo, 57 (1933), 433–475. https://doi.org/10.1007/BF03017586 doi: 10.1007/BF03017586
|