20503

Appears in sequences

• a(n) = smallest number k such that Product_{i=1..k} prime(i)/(prime(i)-1) > n.at n=22A005579
• Number of intersection points of diagonals of an n-gon in general position, plus number of vertices.at n=28A014626
• Denominators of continued fraction convergents to sqrt(86).at n=10A041153
• Denominators of continued fraction convergents to sqrt(344).at n=10A041651
• Denominators of continued fraction convergents to sqrt(774).at n=10A042493
• Numbers having four 1's in base 9.at n=34A043460
• Number of rooted trees with n nodes and 11 leaves.at n=5A055286
• a(n) = 25*n*(n + 1)/2 + 3.at n=40A061793
• Triangular numbers with sum of digits = 10.at n=25A068129
• Triangular numbers whose digit permutations yield at least two further triangular numbers.at n=16A069674
• Triangular numbers in which the sum of the external digits equals the sum of the internal digits.at n=13A088289
• Triangular numbers with palindromic indices.at n=29A089717
• Least triangular number whose digit permutations yield exactly n further triangular numbers.at n=4A095870
• Triangular numbers whose digit reversal is the product of 2 palindromes greater than 1.at n=27A115702
• Triangular numbers equal to the difference between a prime number and its index.at n=33A115887
• Triangular numbers congruent to 1 or 5 mod 6.at n=33A128880
• Values of m such that A139361(n)=4m+1.at n=35A139362
• Triangular numbers n*(n+1)/2 with n and n+1 composite, where number of prime factors in n = number of prime factors in n+1. (Prime factors are counted with multiplicity.)at n=35A144486
• Triangular numbers which are sums of three consecutive primes.at n=6A167788
• a(n+1) = a(n) + floor(a(n)/5) with a(0)=5.at n=48A182306