130305

Appears in sequences

• a(n) = (n^2-1)*(2*n^2-1).at n=16A033595
• Triangular numbers in which the sum of the external digits equals the sum of the internal digits.at n=27A088289
• Row sums of triangle A093922.at n=32A093925
• Triangular numbers for which the sum of the digits is a pentagonal number.at n=33A117305
• a(n) = binomial(2^n-1,2).at n=9A134057
• Triangular numbers t such that all the digits needed to write the consecutive triangular numbers from 0 to t fill exactly an equilateral triangle (no holes, no overlaps).at n=28A158030
• a(n) = ((2^b-1)/phi(n))*Sum_{d|n} Moebius(n/d)*d^(b-1) for b = 9.at n=1A160956
• Triangular numbers which are sums of 5 consecutive primes.at n=12A173421
• Triangle T(n, k) = c(n, q)/c(k, q) if k <= floor(n/2), otherwise c(n, q)/c(n-k, q), where c(n, q) = Product_{j=1..n} (1 - q^j) and q = 2, read by rows.at n=47A174387
• Triangle T(n, k) = c(n, q)/c(k, q) if k <= floor(n/2), otherwise c(n, q)/c(n-k, q), where c(n, q) = Product_{j=1..n} (1 - q^j) and q = 2, read by rows.at n=52A174387
• Number of length 4 arrays x(i), i=1..4 with x(i) in i..i+n and no value appearing more than 3 times.at n=17A250362
• Number of orbits of Aut(Z^7) as function of the infinity norm n of the representative lattice point of the orbit, when the cardinality of the orbit is equal to 80640.at n=36A266396
• Number of holes in a sheet of paper when you fold it n times and cut off the four corners.at n=17A274230
• Three-column array pPT read by rows: subsequence of primitive Pythagorean triples (x, y, z) with x = A153893^2 - A000079^2, y = 2*A153893*A000079, z = A153893^2 + A000079^2, ordered by increasing z.at n=21A334638
• Triangular numbers which are products of five distinct primes.at n=31A357590
• Denominators in a harmonic triangle; q-analog of A126615, here q = 2.at n=43A377278
• Denominators in a harmonic triangle; q-analog of A126615, here q = 2.at n=52A377278