55 five$5+55+555+5555+55555+cdots n$ terms, Sum of finite seqence of this pattern can be obtained by re-arranging this into geometric sequence. $5$ should be taken common55 is a square pyramidal number. 55 is: . the 10th Fibonacci number [1] and the 10th triangular number, [2] The sum of 55's dits is also 10.; the 5th heptagonal number, [3] the 5th square