491402domain: NAppears in sequencesSmallest number strictly greater than previous one which is the sum of squares of two previous distinct terms (a(1)=1, a(2)=2).at n=22A008318Numbers of the form q-p, where p and q are prime and q = p^0+p^1+p^2+..+p^k for some k.at n=26A166388Numbers m such that sigma(m-1) is a prime.at n=27A270413