110 people attended OEIS-50 (videos, suggestions); annual fundraising drive to start soon (donate); editors, please edit! (stack is over 300), your editing is more valuable than any donation.
212 belongs to this sequence because 212 sorted is 122 and the sum of the squares of the digits of 122 = 1^2 + 2^2 + 2^2= 9 and 122 + 9 = 131, a palindrome.