2220778

Appears in sequences

• Numbers k such that k and 10*k are both triangular numbers.at n=7A068085
• a(n) = (9n^4 - 18n^3 + 18n^2 - 9n + 2)/2.at n=26A079903
• Triangular numbers m such that A040115(m) is also triangular.at n=33A087597
• Smallest nonzero n-digit term of A087597, or 0 if no such number exists.at n=6A087599
• Numerator of (9*(n^4 - 2*n^3 + 2*n^2 - n) + 2)/(2*(2*n-1)).at n=26A096430