户籍已迁移，请问要到哪个派出所开”居民身份证证号证明函”，谢谢。

Regarding  opening a "Resident Identity Card Number Certification Letter" after household registration migration, I would suggest the following:

1. You need to go to the police station where your new household registration is located. According to the Ministry of Public Security's regulations, the police station where the new household registration is located is responsible for issuing the "Resident Identity Card Number Certification Letter".

2. Bring your resident ID card and proof of the new address. The new address can be proved by property certificate, rental agreement, etc. These materials are required for the police to verify your identity and current address.

3. Fill in an application form. The police station will provide the application form for the "Resident Identity Card Number Certification Letter". You need to fill in personal information such as name, ID number, address, contact information, and reason for application.

4. Pay the relevant fees. The fee for issuing a "Resident Identity Card Number Certification Letter" is usually a few yuan. The specific standard can be checked on the official website of the local public security bureau or the price list of the police station.

5. Provide a 2-inch bareheaded photo. The photo needs to be taken within the last 6 months with a white background.

6. Certification letter can be obtained on-site. After submitting the relevant materials and paying the fees, the police will review and approve the application on-site. You can obtain the "Resident Identity Card Number Certification Letter" on the same day.

7. Certification letter is valid for 6 months. The validity period of the "Resident Identity Card Number Certification Letter" is 6 months. If it expires, you need to apply again.

I hope the above suggestions can help you apply for the "Resident Identity Card Number Certification Letter" after household registration migration. Let me know if you have any other questions.