276 (two hundred [and] seventy-six) is the natural number following 275 and preceding 277.

276 is the sum of 3 consecutive fifth powers (276 = 1⁵ + 2⁵ + 3⁵).^[1] As a figurate number it is the 23rd triangular number,^[2] a hexagonal number, and a centered pentagonal number, the third number after 1 and 6 to have this combination of properties.^[3]

276 is the size of the largest set of equiangular lines in 23 dimensions. The maximal set of such lines, derived from the Leech lattice, provides the highest dimension in which the "Gerzon bound" of ${\textstyle {\binom {n+1}{2}}}$ is known to be attained; its symmetry group is the third Conway group, Co₃.^[4][5]

276 is the smallest number for which it is not known if the corresponding aliquot sequence either terminates or ends in a repeating cycle.^[6][7] 306 follows the same sequence as 276, since its aliquot sum is the same as 276.