Each week Manhattan GMAT posts a GMAT question on our blog and follows up with the answer the next day. Are you up for the challenge?
For positive integer m, the m-th heptagonal number is given by the formula (5m2 – 3m)/2. For positive integer n, the n-th triangular number is the sum of the first n positive integers. Which of the following is true for k, the smallest triangular number that is also heptagonal?
(A) 33 ? k ? 40
(B) 41 ? k ? 48
(C) 49 ? k ? 56
(D) 57 ? k ? 64
(E) 65 ? k ? 72
