21528

Appears in sequences

• Number of segments (and sides) created by diagonals of an n-gon in general position.at n=21A014628
• a(n) = 25*n*(n + 1)/2 + 3.at n=41A061793
• Triangular numbers which are products of triangular numbers larger than 1.at n=23A068143
• Triangular numbers which are a concatenation of two or more positive triangular numbers.at n=31A068144
• Triangular numbers such that both the number formed by the first floor((k+1)/2) digits and the remaining part (if any) are triangular numbers, where k is the number of digits.at n=13A068821
• Denominator of the generalized harmonic number H(n,5,3).at n=4A075142
• Triangular numbers which are 7-almost primes.at n=11A076581
• Numbers k such that sopfr(k)=tau(k).at n=38A078511
• Numbers k such that 2k-1 divides 2^k-1.at n=15A081856
• Numbers that can be expressed as the difference of the squares of primes in exactly five distinct ways.at n=23A092001
• Triangular numbers equal to the difference between a prime number and its index.at n=34A115887
• Triangular numbers for which the sum of the digits is a heptagonal number.at n=24A117312
• Hexagonal numbers divisible by 6.at n=35A117794
• Row sums of triangle A134392.at n=22A134393
• Product of the nonzero exponents in the prime factorization of n!.at n=27A135291
• Triangular numbers n*(n+1)/2 with n composite, where number of prime factors of n, counted with multiplicity, is less than the number of prime factors in n+1.at n=39A144524
• a(n) = m*(m+1)/2, where m = floor(n^(3/2)).at n=34A185541
• Triangular numbers that are the product of two triangular numbers greater than 1.at n=16A188630
• Triangular numbers k whose divisors can be partitioned into three disjoint sets whose sums are all sigma(k)/3.at n=13A206025
• a(n) = Sum_{i=0..n} digsum(i)^3, where digsum(i) = A007953(i).at n=48A231688