something interesting
http://www.computerbasedmath.org/
wolframalpha
blogs:
http://sillyrobot.ixiezi.com/index.php/archives/category/oi/oj-prob-sol/spoj
http://www.cnblogs.com/nyroro/articles/2459100.html
http://2hspsr.9966.org/index.asp?difficulty=0
fotile96:http://www.2333333.tk/
数论专场:http://blog.csdn.net/wxfwxf328/article/details/7611961
SPOJ:
MSKYCODE VGCD LCMSUM GCDEX SEQAGAIN(带乘法和乘方的递推式) GCDSQF
BZOJ
[SCOI2012]奇怪的游戏 [JSOI]括号序列
tsin 楼房重建(树套数?)
DIVSUM
http://1tthinking.com/2011/03/22/%E7%A5%9E%E5%A5%87%E7%9A%84%E9%A2%84%E5%A4%84%E7%90%86