17940

Appears in sequences

• a(n) = floor(n(n-1)(n-2)(n-3)/20).at n=26A011930
• Number of segments created by diagonals of n-gon.at n=20A014629
• Number of partitions satisfying 0 < cn(0,5) + cn(1,5) + cn(2,5) + cn(3,5) and 0 < cn(0,5) + cn(4,5) + cn(2,5) + cn(3,5).at n=36A039903
• Numbers k such that the sign of core(k)-phi(k) is not equal to 2*mu(k)^2-1, where core(k) is the squarefree part of k.at n=30A070237
• Numbers k such that the number of steps to reach 1 in '3x+1' problem equals tau(k), the number of divisors of k.at n=25A070980
• Integers k such that omega(k) = omega(k-1) + omega(k-2) + omega(k-3), where omega(n) is the number of distinct prime factors of n.at n=10A076252
• Numbers k such that sopfr(k)=tau(k).at n=32A078511
• Record-setting differences between adjacent elements of the Mian-Chowla sequence A005282.at n=37A080222
• a(1)=1, a(n)=ceiling(n/(n+1)*sum(k=1,n-1,a(k))).at n=16A082423
• Numbers whose number of divisors equals the sum of their separate prime-power decompositions.at n=8A087004
• Numbers n such that primitive solutions for 1/n^2 = 1/x^2 + 1/y^2 exist.at n=40A094807
• Size |S| of the largest subset S of {0,1}^n whose measure m(S) is <= 2^n, where m is the additive measure defined on each element x of S by m({x}) = 2^k(x), where k(x) is the number of non-null coordinates of x.at n=19A115993
• Numbers k such that k divides 1 + Sum_{j=1..k} prime(j)^2 = 1 + A024450(k).at n=23A128166
• A transform of the Catalan numbers.at n=27A157125
• The smallest magic constant of an n X n magic square with distinct prime entries.at n=15A164843
• Numbers such that each digit from 0 to 9 appears at least 7 times in the digits of their divisors.at n=14A175507
• Numbers with prime factorization pqrst^2.at n=29A189983
• 23 times triangular numbers.at n=39A195039
• Number of (w,x,y,z) with all terms in {1,...,n} and w+x<2y+2z.at n=12A212562
• Number of (w,x,y) with all terms in {0,...,n} and |w-x| + |x-y| > w+x+y.at n=26A213482