<Table> <Tr> <Th_colspan="2"> United States Congress </Th> </Tr> <Tr> <Td_colspan="2"> 115th United States Congress </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Th_colspan="2"> Type </Th> </Tr> <Tr> <Th> Type </Th> <Td> Bicameral </Td> </Tr> <Tr> <Th> Houses </Th> <Td> Senate House of Representatives </Td> </Tr> <Tr> <Th_colspan="2"> History </Th> </Tr> <Tr> <Th> Founded </Th> <Td> March 4, 1789 (228 years ago) (1789 - 03 - 04) </Td> </Tr> <Tr> <Th> Preceded by </Th> <Td> Congress of the Confederation </Td> </Tr> <Tr> <Th> New session started </Th> <Td> January 3, 2017 </Td> </Tr> <Tr> <Th_colspan="2"> Leadership </Th> </Tr> <Tr> <Th> President of the Senate & Vice President </Th> <Td> Mike Pence (R) Since January 20, 2017 </Td> </Tr> <Tr> <Th> Speaker of the House of Representatives </Th> <Td> Paul Ryan (R) Since October 29, 2015 </Td> </Tr> <Tr> <Th> President pro tempore of the Senate </Th> <Td> Orrin Hatch (R) Since January 6, 2015 </Td> </Tr> <Tr> <Th_colspan="2"> Structure </Th> </Tr> <Tr> <Th> Seats </Th> <Td> <P> 535 voting members </P> <Ul> <Li> 100 senators </Li> <Li> 435 representatives </Li> </Ul> 6 non-voting members </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Th> Senate political groups </Th> <Td> <Ul> <Li> Republican (51) </Li> <Li> Democratic (47) </Li> <Li> Independent (2) (caucusing with Democrats) </Li> </Ul> </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Th> House of Representatives political groups </Th> <Td> <Ul> <Li> Republican (239) </Li> <Li> Democratic (193) </Li> <Li> Vacant (3) </Li> </Ul> </Td> </Tr> <Tr> <Th_colspan="2"> Elections </Th> </Tr> <Tr> <Th> Senate last election </Th> <Td> November 8, 2016 </Td> </Tr> <Tr> <Th> House of Representatives last election </Th> <Td> November 8, 2016 </Td> </Tr> <Tr> <Th_colspan="2"> Meeting place </Th> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Td_colspan="2"> United States Capitol Washington, D.C., United States </Td> </Tr> <Tr> <Th_colspan="2"> Website </Th> </Tr> <Tr> <Td_colspan="2"> www.congress.gov </Td> </Tr> </Table> <Tr> <Th_colspan="2"> United States Congress </Th> </Tr>

How many senators are there in united states