A307830 - OEIS

A307830

Numbers k for which there exist no palindromic decagonal numbers (also known as 10-gonals) of length k.

2, 4, 6, 7, 9, 11, 16, 18, 19

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..9.

P. De Geest, Palindromic decagonals

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

Cf. A001107, A082722, A307827, A307829.

Sequence in context: A375496 A139529 A341291 * A157202 A282896 A141437

Adjacent sequences: A307827 A307828 A307829 * A307831 A307832 A307833

KEYWORD

nonn,base,hard

AUTHOR

Robert Price, Apr 30 2019

STATUS

approved