135173domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumbers k such that k and the k-th triangular number T(k) = k*(k+1)/2 have only odd digits.at n=13A347475Least n-digit number k with only odd digits such that the k-th triangular number also has only odd digits.at n=5A349247Prime numbersat n=12590