126253

Appears in sequences

• Lexicographically earliest sequence of pairwise coprime triangular numbers.at n=23A034792
• Triangular numbers which are the product of two primes.at n=30A068443
• Triangular numbers that are also brilliant (A078972).at n=23A113940
• Semiprimes in A006987(n), or semiprime binomial coefficients: C(n,k), 2 <= k <= n-2.at n=31A124000
• Product p*q of two primes with q = 2*p + 1.at n=17A156592
• Semiprimes of form p*q with p < q, such that 2^p - 1 == 0 (mod q).at n=20A179768
• Numbers n such that A229964(n) = 1.at n=20A229965
• Squarefree numbers (from A005117) with prime divisors in a 2p+1 progression.at n=23A231966
• Numbers n with the property that the symmetric representation of sigma(n) has four parts, each of width one and two regions meet at the center of the Dyck path.at n=27A264104
• The first of three consecutive triangular numbers the sum of which is equal to the sum of three consecutive primes.at n=36A298168
• Triangular numbers that are the product of two distinct prime numbers of the form 4*k + 3.at n=8A365849
• a(n) = 1 + Sum_{k=0..n-1} (2*k+1) * a(k) * a(n-k-1).at n=6A376125