51681

Appears in sequences

• Triangular numbers with sum of digits = 21.at n=31A068131
• Triangular numbers in which the k-th significant digit either divides k or is a multiple of k.at n=27A069559
• Triangular numbers for which the sum of the digits is an octagonal number.at n=34A117523
• Triangular numbers t which are average of two consecutive primes p and p+4.at n=31A129752
• Triangular numbers t such that t+10 is a prime.at n=40A129755
• a(n) = (2*n - 1)*(24*n^2 - 42*n + 19).at n=10A160174
• The function W_n(6) (see Borwein et al. reference for definition).at n=20A169711
• Triangular numbers n such that sigma(n) is a square number.at n=11A256151
• Triangular numbers (A000217) that are the sum of seven consecutive triangular numbers.at n=2A257711
• Triangular numbers k such that psi(k) is a square, where psi(k) is the Dedekind psi function (A001615).at n=23A292064
• Solution of the complementary equation a(n) = a(n-1) + a(n-2) + b(n-1) - b(n-2) + 1, where a(0) = 1, a(1) = 3, b(0) = 2, b(1) = 4.at n=20A294422
• a(n) = n*Fibonacci(n-2) + ((-1)^n + 1)/2.at n=20A323812
• a(n) is the least positive number k that can be written in exactly k ways as (x*y+1)*(x*z+1) with x > y > z > 1.at n=7A345215
• Triangular numbers that in base 2 have the same number of 0's and 1's.at n=37A345348
• Numbers that start a run of four consecutive triangular numbers with four distinct prime factors.at n=11A349773
• Triangular numbers that are the sum of two distinct nonzero triangular numbers in exactly two ways.at n=18A350368
• Number of distinct lines passing through exactly two points in a triangular grid of side n.at n=32A362014
• Hexagonal numbers that are products of exactly four distinct primes.at n=26A381920