document.write( "Question 1039348: Which of the following is divisible by 13?
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Algebra.Com's Answer #654090 by ikleyn(52862) $\"\"$ $\"About$

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document.write( "1. It was solved before in https://www.algebra.com/algebra/homework/divisibility/Divisibility_and_Prime_Numbers.faq.question.1038874.html\r\n" );
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document.write( "2. In order to find that 15! -1 is not divisible by 13, there is no need to calculate this number and then make division.\r\n" );
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document.write( "   Simply 15! contains 13 as a factor, therefore 15! is a multiple of 13.\r\n" );
document.write( "   Hence, the previous number 15! - 1 is not a multiple of 13.\r\n" );
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document.write( "3. Same logic works for 14! + 1.\r\n" );
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document.write( "4. By answering these questions in https://www.algebra.com/algebra/homework/divisibility/Divisibility_and_Prime_Numbers.faq.question.1038874.html \r\n" );
document.write( "   I assumed that it it obvious.\r\n" );
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