191271domain: NAppears in sequencesa(n) = p(n)*(p(n)-1)/2 where p(n) = upper member of n-th pair of twin primes.at n=27A082669Triangular numbers T such that T+10 is the next prime after T.at n=27A129540Triangular numbers that are repdigits with length > 2 in some base.at n=37A274084