A Q&A community typically employs various types of external incentives to motivate knowledge contribution from their community members. This study aims to examine the effects of different external incentives, which are conceptualized as different types of motivational factors, on community participants’ sustained knowledge contribution. Drawing on motivation crowding theory, the present study proposes that different motivators interact and jointly influence knowledge contribution behavior. The panel data were collected from a Chinese Q&A community by using the Python Scrapy crawler, and the Poisson regression model with fixed effects was used to validate the integrative model. The results revealed that generalized reciprocity and social learning undermined the effect of online attractiveness on sustained knowledge contribution, whereas peer feedback strengthens this effect. The findings contribute to the extant research on sustained contribution behavior and provide practical insights into sustaining virtual communities.

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Orthomorphic permutations have important application in the design of cryptosystems. Based on the one-to-one corresponding relationship between orthomorphic permutations and orthomorphic permutation polynomials, this paper studies orthomorphic permutation polynomials of degree 2 d +1 over finite field F 2 n. By the congruence theory and the distributive law of degrees for multiplying polynomials, the necessary condition that the polynomials of degree 2 d +1 are orthomorphism is obtained exactly. Meanwhile, this paper proves that there does not exist orthomorphic permutation polynomials of degree 5 over finite field F 2 n. The above results not only provide a method to judge orthomorphic permutation polynomials, but also make a contribution to the enumeration of the kind of polynomials.