4020030domain: NAppears in sequencesNumbers k such that 2^k == -1 (mod k-1).at n=24A055685Numbers k such that 11^k == -1 (mod k-1).at n=30A055694Triangular numbers divisible by the square of the sum of their digits.at n=29A243008Triangular numbers whose sum of digits is 9.at n=33A375824