Question

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Answer 1

21.2 l (1^n +2^n+3^n)

uc pt. 1^n=1

uc pt. 2^n={2;4;8;6}

uc.pt.3^n={3;9;7;1}

uc pt. 1^n +3^n = număr par

2^n uc. nr.par=>2 este divide expresia

22.(1^n +2^n+3^n+4^n):10. n≠4

uc pt. 1^n=1

uc pt. 2^n={2;4;8;6}

uc.pt.3^n={3;9;7;1}

uc pt.4^n={4;6;4;6}

uc (1^n +2^n+3^n+4^n)=0

=>(1^n +2^n+3^n+4^n)divizibila cu 10.