82621

Appears in sequences

• Doubly triangular numbers: a(n) = n*(n+1)*(n^2+n+2)/8.at n=28A002817
• 9-gonal (or nonagonal) triangular numbers.at n=2A048909
• Iterated triangular numbers with seed 7.at n=3A050548
• Triply triangular numbers.at n=7A064322
• Triangular numbers which are one more than a product of distinct triangular numbers.at n=30A083517
• Triangular numbers m such that A040115(m) is also triangular.at n=27A087597
• Largest n-digit term of A087597, or 0 if no such number exists.at n=4A087600
• a(n) = (n+1)(n+2)(n+3)(2n+3)(10n^2 + 27n + 20)/360.at n=9A108673
• Tree generated by the triangular numbers: a(1) = 1; a(2n) = nontriangular(a(n)), a(2n+1) = triangular(a(n+1)), where triangular = A000217, nontriangular = A014132.at n=56A183079
• a(n) = A185128(n) - A185129(n).at n=11A185253
• Numbers n for which phi(n)=sigma(n'), where phi is the Euler totient function, sigma is the sum of divisors and n' the arithmetic derivative of n.at n=14A189057
• a(n) = n*(7*n - 5)*(49*n^2 - 35*n - 10)/8.at n=7A264894
• Integers k such that A000330(k) is the sum of 2 positive cubes.at n=8A269842
• Numbers n such that the decimal expansion of n^2 contains n+1.at n=14A282384
• Composite numbers n such that E(n+1)+1 is divisible by n, where E(n) is the n-th Euler number (A122045).at n=37A287934
• Table read by rows. T(n, k) = (-1)^(n - k) * Sum_{j=k..n} binomial(n, j) * A354794(j, k) * j^(n - j).at n=31A359759
• Numbers k such that (2^k-1)^k == 1 (mod (2^k+1)*k^2) and 2^(k-1) != 1 (mod k).at n=3A384148