Illya Gerasymchuk

Illya Gerasymchuk is a financial and software engineer who builds full-stack consumer and financial software, from quantitative modeling and market microstructure to cryptographic protocols and agentic AI. He is a senior software engineer at Revolut (Retail & AI), contributes to open source including IETF TLS 1.3 and…

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Demystifying the regular expression that checks if a number is prime (2016)

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Ever wondered how the ^.?$|^(..+?)\1+$ regular expression can tell you if a number is not prime? In this blog post you'll learn how and why it works. Code examples in Java, JavaScript, Python and Perl are provided.