Fix primes on RSA key conversion #729

Job	Run time
no_std (1.65.0, thumbv7em-none-eabi)	9m 35s
build (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mul...	54s
no_std (1.65.0, wasm32-unknown-unknown)	9m 30s
test (1.65.0)	26m 41s
build (x86_64-apple-darwin, macos-latest, stable)	48s
no_std (stable, thumbv7em-none-eabi)	6m 27s
test (stable)	19m 7s
build (x86_64-pc-windows-msvc, windows-latest, stable)	1m 12s
no_std (stable, wasm32-unknown-unknown)	6m 5s
minimal-versions / minimal-versions	53s
	1h 21m 12s

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