18915

Appears in sequences

• a(1) = 9; a(n+1) = smallest triangular number > a(n) formed by adding at least one digit to a(n).at n=3A068624
• Triangular numbers in which the k-th significant digit either divides k or is a multiple of k.at n=26A069559
• Triangle read by rows: d(n,k) = number of decreasing labeled trees with n nodes and largest leaf <= k, for 1 <= k <= n.at n=47A079268
• Third row of Pascal-(1,6,1) array A081581.at n=28A081591
• Triangle read by rows in which the n-th row contains the n smallest triangular numbers with the least significant digits of the n-th triangular number.at n=13A095225
• Numbers k such that phi(k)*sigma(k) is a cube.at n=9A114077
• Number of permutations of length n which avoid the patterns 1432, 2134, 4132; or avoid the patterns 3124, 4123, 4321.at n=9A116773
• Numbers which are both lucky and triangular.at n=35A118565
• Triangular numbers that can be written as sum of three positive cubes.at n=39A119977
• Triangle T(n,k) = total of number at last index for all set partitions of n into k parts.at n=47A120095
• Triangular numbers t which are average of two consecutive primes p and p+4.at n=22A129752
• 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=35A144524
• Numbers that are repdigits with length > 2 in more than one base.at n=38A167783
• T(n,m) = number of 0..m-1 integer arrays v[1..n] of length n with all autocorrelation values sum(i){v[i]*v[i-k]} distinct for k in 0..n-1.at n=62A171307
• Number of 0..3 integer arrays v[1..n] of length n with all autocorrelation values sum(i){v[i]*v[i-k]} distinct for k in 0..n-1.at n=7A171309
• Number of 0..n-1 integer arrays v[1..8] of length 8 with all autocorrelation values sum(i){v[i]*v[i-k]} distinct for k in 0..7.at n=3A171359
• Triangular numbers T such that T+2 is a prime.at n=37A171570
• Numbers k such that k-4, k-2, k+2 and k+4 are prime.at n=17A173037
• E.g.f. A(x), where A(x)=x*exp(A(x))+x*log(1/(1-A(x))).at n=5A185388
• Total number of different letters summed over all ternary words of length n.at n=8A210448