Hey,

There is no specific post as a mathematician in UPSC. Also, I would suggest you not to continue maths, since you don't like it. You may feel like you can solve any problem for now, but there will be problems that you won't be able to solve if you choose maths as your profession. The services  provided by UPSC are as follows:

All India services:

1. .IAS
2. Indian Forest Services (IFoS)
3. IIPS

Central service group A:

• (IFS)
• Indian P&T Accounts and Finance Services (IP&TAFS)
• Indian Audit and Accounts Service(IA&AS)
• Indian Civil Accounts Service(ICAS)
• Indian Corporate Law Service(ICLS)
• Indian Defence Accounts Service(IDAS)
• Indian Defence Estates Service(IDES)
• Indian Information Service (IIS)
• Indian Ordnance Factories Service(IOFS)
• Indian Postal  (IPSer.vicoS)
• Indian Railway Accounts Service(IRAS)
• Indian Railway Personnel Service(IRPS)
• Indian Railway Traffic Service(IRTS)
• Indian Revenue Service (IRS-IT)
• Indian Revenue Service (IRS-C&CE)
• Indian Trade Service (ITrS)
• Railway Protection Force (RPF)

Group B:

• Armed Forces Headquarters Civil Services (AFHCS)
• Delhi, Andaman and Nicobar Islands Civil Service (DANICS)
• Delhi, Andaman and Nicobar Islands Police Service (DANIPS)
• Pondicherry Civil Service (PCS)
• Pondicherry Police Service (PPS

You can choose from these posts as per your interest.

Hope this helps!