login
A307830
Numbers k for which there exist no palindromic decagonal numbers (also known as 10-gonals) of length k.
2
2, 4, 6, 7, 9, 11, 16, 18, 19
OFFSET
1,1
MATHEMATICA
A307827 = {0, 1, 232, 27972, 76867, 25555552, 7154664517, 158229922851, 2028787878202, 2040061600402, 2733623263372, 52667666676625, 675972505279576, 28519896169891582, 73542836563824537, 74529570707592547, 25552469511596425552, 27835145788754153872, 62740719088091704726, 67047523077032574076, 77979812588521897977, 107838025535520838701};
a[n_] := Length[Select[A307827, IntegerLength[#] == n || (n == 1 && # == 0) &]];
Select[Range[20], a[#] == 0 &]
CROSSREFS
KEYWORD
nonn,base,hard
AUTHOR
Robert Price, Apr 30 2019
STATUS
approved