求自然数的方幂和是一个经典问题,设 Sk(n) 表示 \sigmam-1n m4, Schwlts 和Scott 都通过复杂的计算给出了当1 \leq k \leq 6 及 7 \leq k \leq 13时 Sk(n) 的计算公式。本文用初等的方法给出了1 \leq k \leq 30时 Sk(n) 的计算公式。
Let ϕ be a generalized Orlicz function satisfying (A0), (A1), (A2), (aInc) and (aDec). We prove that the mapping
f →f #:=supB 1/\int|B||f(x)-fB|dx is continuous on Lϕ(·)(Rn) by extrapolation. Based on this result we generalize Korn’s inequality to the setting of generalized Orlicz spaces, i.e., ||\triangledown f||L^{ϕ(·)}(Ω) \lesssim||DF|||L^{ϕ}(Ω) . Using the Calder´on–Zygmund theory on generalized Orlicz spaces, we obtain that the divergence equation divu=f has a solution u∈(W01,ϕ(·)(Ω))n such that ||\triangledown u||L^{ϕ(·)}(Ω) \lesssim ||f||L^{ϕ}(Ω).