document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=713629>Question 713629</A>: <I><SPAN STYLE=\"word-break: break-all;\"> write the rule for the sequence 2, 9, 21, 38,...\r<BR>\n" );
document.write( "\n" );
document.write( "I was recently given an answer but one of the differences that I was given was wrong\r<BR>\n" );
document.write( "\n" );
document.write( "Someone gave me 9-21= 11 That would be wrong so would there be a pattern and formula </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #438804 by </B><A HREF=/tutors/aboutme.mpl?userid=kevwill><B>kevwill(135)</B></A><img src=\"/images/stars/stars-09.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=kevwill><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=kevwill><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=438804\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> From the sequence:<BR>\n" );
document.write( " <BR>\n" );
document.write( "2, 9, 21, 38, ..., <BR>\n" );
document.write( " <BR>\n" );
document.write( "the differences between terms are:<BR>\n" );
document.write( " <BR>\n" );
document.write( "7, 12, 17, ... <BR>\n" );
document.write( "  <BR>\n" );
document.write( "and the second level differences are:<BR>\n" );
document.write( " <BR>\n" );
document.write( "5, 5, 5, ...<BR>\n" );
document.write( " <BR>\n" );
document.write( "So we know that the first term of the formula is <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%285%2F2%29%2An%5E2 ALIGN=MIDDLE  ALT=\"%285%2F2%29%2An%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" >.  A little experimentation shows that the actual formula is:<BR>\n" );
document.write( " <BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%285%2An%5E2+-+n%29%2F2 ALIGN=MIDDLE  ALT=\"%285%2An%5E2+-+n%29%2F2\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( " <BR>\n" );
document.write( "So the sequence continues<BR>\n" );
document.write( " <BR>\n" );
document.write( "2, 9, 21, 38, 60, 87, 119, ...<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );