27.3 Pentagonal numbers 721
27.3 Pentagonal numbers ..................
The pentagonal numbers are the sums of the arithmetic progression
1+4+7+···+(3n−2) +···Thenth pentagonal number isPn=^12 n(3n−1).
Palindromic pentagonal numbers
nPn nPn nPn
11101 12521 6010 54177145
25693 720027 26466 1050660501
422 2173 7081807 26906 1085885801
26 1001 2229 7451547 31926 1528888251
44 2882 4228 26811862 44059 2911771192