C28 I Am Studying Goldbach's Conjecture

"Qin Luo, get up and tell me how you solved this question." At this moment, Lee Wei's "kind" words pulled Qin Luo back to reality.

Record SN was the first N of the equal-difference series and always A1-7S3 = -15.

(1) Seek the general formula of 'An'.

(2) Ask for SN, and ask for the minimum value of SN.

This was the problem of the smallest value of an equal-rank number