27495

Appears in sequences

• a(n) = Sum_{i=0..n} Sum_{j=0..n} T(i,j), T given by A026725.at n=13A026734
• a(n) = 49*(n*(n+1)/2) + 6.at n=33A061792
• Triangular matrix T, read by rows, that satisfies: T^2 + 2*T = SHIFTUP(T), also T^(n+1) + 2*T^n = SHIFTUP(T^n - D*T^(n-1)) for all n, where D is a diagonal matrix with diagonal(D) = diagonal(T) = {1,2,3,...}.at n=23A103236
• Triangular numbers equal to the difference between a prime number and its index.at n=40A115887
• Triangular numbers for which the sum of the digits is a cube.at n=9A117803
• a(n) = 3*n*(6*n + 1).at n=39A144314
• a(n) = m*(m+1)/2, where m = floor(n^(3/2)).at n=37A185541
• Triangular numbers which become primes when their rightmost digit is removed.at n=30A227936
• Triangular numbers which have one or more occurrences of exactly five different digits.at n=17A241788
• Triangular numbers T such that both (T+2) and (T-2) are semiprimes.at n=33A242356
• Let s denote the sum of the deficient numbers in the aliquot parts of x. Sequence lists numbers x such that sigma(s) = usigma(x), where usigma(x) is the sum of the unitary divisors of x (A034448).at n=10A258134
• Numbers that start a run of four consecutive triangular numbers with four distinct prime factors.at n=5A349773
• Second hexagonal numbers having middle divisors.at n=40A361209
• Number of chordless cycles in the complement of the n-Sierpinski gasket graph.at n=4A370299
• a(n) is the maximal determinant of an n X n symmetric Toeplitz matrix having 0 on the main diagonal and all the integers 1, 2, ..., n-1 off-diagonal.at n=6A374280
• a(n) is the maximal absolute value of the determinant of an n X n symmetric Toeplitz matrix having 0 on the main diagonal and all the integers 1, 2, ..., n-1 off-diagonal.at n=6A374281