document.write( "Question 1017771: what is the rule for 12, 40, 90, 168, 280, 432 \n" ); document.write( "
Algebra.Com's Answer #633992 by Edwin McCravy(20056)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "12, 40, 90, 168, 280, 432\r\n" );
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document.write( "I first tried dividing them by \r\n" );
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document.write( "1, 2, 3, 4, 5, 6 \r\n" );
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document.write( "respectively and got\r\n" );
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document.write( "12, 20, 45, 42, 56, 72\r\n" );
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document.write( "Then I recognized that as the pattern:\r\n" );
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document.write( "3∙4, 4∙5, 5∙6, 6∙7, 7∙8, 8∙9\r\n" );
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document.write( "So the sequence is:\r\n" );
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document.write( "1∙3∙4, 2∙4∙5, 3∙5∙6, 4∙6∙7, 5∙7∙8, 6∙8∙9\r\n" );
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document.write( "So it is:\r\n" );
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document.write( "an = n(n+2)(n+3)\r\n" );
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document.write( "a1 = 1(1+2)(1+3) = 1(3)(4) = 12\r\n" );
document.write( "a2 = 2(2+2)(2+3) = 2(4)(5) = 40\r\n" );
document.write( "a3 = 3(3+2)(3+3) = 3(5)(6) = 90\r\n" );
document.write( "a4 = 4(4+2)(4+3) = 4(6)(7) = 168\r\n" );
document.write( "a5 = 5(5+2)(5+3) = 5(7)(8) = 280\r\n" );
document.write( "a6 = 6(6+2)(6+3) = 6(8)(9) = 432\r\n" );
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document.write( "Edwin
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