A) An octagonal number, and as the sum of the first four pentagonal numbers, it is a pentagonal pyramidal number.
B) A Wedderburn–Etherington number and a centered decagonal number; its reciprocal has period 10; it is the smallest number with this period reciprocal length.
C) A composite number, and the smallest number with exactly six divisors
D) A Giuga number
I believe this cache is also handi-cachable. So fun for all! Please kindly alert me if my assuming is wrong!
