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Proofs of power sum and binomial coefficient congruences via Pascal’s identity. (English) Zbl 1230.05014
Summary: A well-known and frequently cited congruence for power sums is $1^n+ 2^n+\cdots+ p^n\equiv\begin{cases} -1\pmod p\;&\text{if }(p-1)\mid n,\\ 0\pmod p\;&\text{if }(p-1)\nmid n,\end{cases}$ where $$n\geq 1$$ and $$p$$ is prime. We survey the main ingredients in several known proofs. Then we give an elementary proof, using an identity for power sums proven by B. Pascal in the year 1654. An application is a simple proof of a congruence for certain sums of binomial coefficients, due to Ch. Hermite [J. Reine Angew. Math. 81, 93–95 (1875; JFM 07.0131.01)] and P. Bachmann [Niedere Zahlentheorie. Zweiter Teil, Teubner, Leipzig (1910; JFM 41.0221.10) (p. 53); Reprint. Bronx, N. Y.: Chelsea (1968; Zbl 0253.10001)].

##### MSC:
 11A07 Congruences; primitive roots; residue systems 11B65 Binomial coefficients; factorials; $$q$$-identities 05A10 Factorials, binomial coefficients, combinatorial functions 05A19 Combinatorial identities, bijective combinatorics
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