276

276 is the sum of 3 consecutive fifth powers (276 = 15 + 25 + 35). As a figurate number it is the 23rd triangular number, a hexagonal number, and a centered pentagonal number, the third number after 1 and 6 to have this combination of properties. 276 is the first triangular number that can be arrived at in three ways by adding pairs of triangular numbers together. This sequence, dubbed'Triple Triangle-Pair Numbers' is the sequence of integers: 276, 406, 666, ...