a（n）=T（n，21）；T（n，k）=和{i=1..n}二项式（n+1，i）*二项式。
a（n）=（n+1）*二项式（n+20，21）*超几何3F2（[-20，-n，1-n]，[2，-n-20]，1）。
a（n）=（538257874440/42！）*n*（n+1）*（1242992558091884813937662754816000000+32881835036602546028491571200000000*n+574832876343303230896837500224000000*n^2+56870188257495290129141765945425920000*n^3+4880652187310657147635733626880000*n^4+27924891657758813405892359858432000*n^5+15433852148314741971664420691673088000*n*n^6+5922795934469650476199817 194266年705920*n^7+23633263646950664110615399338389323776*n^8+6557497088125611042892906739292800*n^9+20148036119845933104915307520*n^10+42270110248833238367203562820695040*n^11+104284338041749995423701069631220992*n^12+170250528042078685582014815227260*n^13+347378992461285895698788698610560*n^14+（+）449827918639409055961252979192960*n^15+777602697715487702683123150572128*n^16+8071528554520601160114398770800*n^17+1977934223854188918636742220*n^18+1008310281537694045482337773800*n^19+130493062980868383096447853569*n^20+892237320110273631864787000*n^21+10185173737197591285675901050*n^22+56547711034611195278152900*n^23+574799001272234774582445*编号24+25804389773082709176000*编号25+235455801452942771200*编号26+84727901572097480*编号27+6988357410155794*编号28+198659321097901200*编号29+14901112723277580*编号30+327062325560360*编号31+22429224033778*编号32+36602803600*编号33+23094295940*编号34+264617940*编号35+153777 517*n^36+110200*n^37+5930*n^38+20*n=39+n^40）。
总尺寸：2*x*（1+20*x+400*x^2+3800*x^3+36100*x^4+216600*x*x^5+1299600*x^6+552330*x^7+23474025*x^8+75116880*x^9+240374016*x^10+600935040*x^11+1502337600*x^12+3004675200*xx^13+6009350.400*x^14+9765194400*x^15+15868440900*x^16+21157921200*x|x^17+28210561600*x^18+31031617760*x^19+34134779536*x^20+3103117760*x^21+28210561600*x^22+21157921200*x^23+15868440900*x^24+9765194400*x^25+6009350400*x^26+3004675200*x^27+1502337600*x^28+6009350.40*x^29+240374016*x^30+75116880*x*^31+23474025*x^32+5523300*xs^33+1299600*xx^34+216600*x*x^35+36100*x^36+3800*x^36+380*x^37+400*x^38+20*x|39+x^40）/（1-x）^43。（结束）
