OFFSET
1,3
COMMENTS
A double palindrome is the concatenation of two palindromes. Permuting the symbols will not change the structure.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
EXAMPLE
For n = 4, the 7 structures are: aaab, aaba, aabb, abaa, abab, abba, abbb.
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Oct 25 2019
STATUS
approved