645248domain: NAppears in sequencesNumbers with prime signature {7,2}, i.e., of form p^7*q^2 with p and q distinct primes.at n=25A179689Numbers k such that k^k == 1 (mod sigma(k)).at n=28A181476Primitive coreful Zumkeller numbers: coreful Zumkeller numbers (A339979) having no coreful Zumkeller aliquot divisor.at n=26A339981