2 problems

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Wu's divisibility-by-3 conjecture for appended-digit primes
Wu's divisibility-by-3 conjecture. If $c(n)=0$ , then $n$ is divisible by $3$ .
Conjectureopendigit-concatenation number-theory primalityarXiv posted 2 days ago
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The OEIS A256480 conjecture for prepended-digit primes
OEIS A256480 conjecture.
Conjectureopendigit-concatenation number-theory primalityarXiv posted 2 days ago

Wu's divisibility-by-3 conjecture for appended-digit primes