18135

Appears in sequences

• a(n) = s(1)t(n) + s(2)t(n-1) + ... + s(k)t(n+1-k), where k = [ (n+1)/2 ], s = (Lucas numbers), t = A000201 (lower Wythoff sequence).at n=22A024474
• Numbers k that divide the (left) concatenation of all numbers <= k written in base 19 (most significant digit on left).at n=42A029488
• Numerators of continued fraction convergents to sqrt(377).at n=5A041714
• a(n) = 3*n*(4*n-1).at n=39A062783
• Numbers k such that (1/k) * Sum_{d|k} d*sigma(d) is an integer.at n=10A069520
• Largest member of the n-th row of the triangular triangle (A093445).at n=44A093446
• Diagonal sums of triangle A185384.at n=9A208481
• Least m>0 for which m*n^2 + 1 is a square and m*triangular(n) + 1 is a triangular number (A000217). Or -1 if no such m exists.at n=3A267077
• Numbers k such that (47*10^k + 133)/9 is prime.at n=21A285379
• a(n) = Sum_{d|n} d^3*A000593(n/d).at n=23A288419
• Numbers k such that phi(x) = 12*k+2 is solvable, where phi is Euler's totient A000010.at n=24A289364
• Numbers m such that the numerator of Sum_{k=1..m, gcd(k,m) = 1} 1/k is divisible by m^3.at n=42A290815
• Numbers m such that the numerator of Sum_{k=1..m, gcd(k,m) = 1} 1/k^2 is divisible by m^2.at n=54A309696
• Number of meanders of length n with Dyck-steps avoiding the consecutive steps UDU and DUD.at n=24A329703
• Odd numbers m for which A379113(m^2) > 1, i.e., k = m^2 has a proper unitary divisor d > 1 such that A048720(A065621(sigma(d)),sigma(k/d)) is equal to sigma(k).at n=35A379122
• Odd nonsquarefree numbers k such that {sum of unitary divisors of k} plus {sum of squarefree divisors of k} >= 2*k.at n=45A389079