34453

Appears in sequences

• Lexicographically earliest sequence of pairwise coprime triangular numbers.at n=14A034792
• a(n) = 49*(n*(n+1)/2) + 6.at n=37A061792
• Triangular numbers which are the product of two primes.at n=19A068443
• a(1) = 0, then smallest triangular number such that a(n+1)- a(n) is a palindrome.at n=24A075057
• Triangular numbers with palindromic indices.at n=35A089717
• Triangular numbers that are also brilliant (A078972).at n=12A113940
• Start with 1 and repeatedly reverse the digits and add 36 to get the next term.at n=37A118536
• Triangular numbers composed of digits {3,4,5}.at n=4A119182
• Triangular numbers with at most two distinct prime factors.at n=41A119663
• Semiprimes in A006987(n), or semiprime binomial coefficients: C(n,k), 2 <= k <= n-2.at n=20A124000
• Product p*q of two primes with q = 2*p + 1.at n=11A156592
• Semiprimes of form p*q with p < q, such that 2^p - 1 == 0 (mod q).at n=13A179768
• a(n) = m*(m+1)/2, where m = floor(n^(3/2)).at n=40A185541
• Base-9 Keith numbers.at n=32A188200
• Triangular numbers T from A000217 such that (4*T+1)/13 is prime.at n=13A208294
• Primitive numbers in A229307.at n=27A229311
• Numbers n such that A229964(n) = 1.at n=14A229965
• Squarefree numbers (from A005117) with prime divisors in a 2p+1 progression.at n=15A231966
• Consider a non-palindromic number of k digits n = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + … + d_(2)*10 + d_(1). Sequence lists the numbers n such that Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(j)*10^(j-1)})} = Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(k-j+1)*10^(i-j)})} (see example below).at n=8A241502
• 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=17A264104