A328693 Number of double palindrome structures of length n using a maximum of four different symbols.

1, 1, 2, 4, 10, 21, 50, 99, 246, 445, 1157, 2047, 5326, 9283, 24453, 41859, 110486, 187851, 494411, 834975, 2190965, 3680541, 9626773, 16101703, 41973942, 69956171, 181823735, 302099557, 783084053, 1297675587, 3355767395, 5548173975, 14317233046, 23623397329, 60846853307

Offset

0,3

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 = 0..200

Formula

a(n) = Sum_{k=1..4} A284877(n,k) for n > 0.

a(n) = A328690(n) + A328692(n).

Crossrefs

Cf. A284877, A328690, A328692.

Sequence in context: A328692 A255711 A204804 * A165136 A165137 A065023

Adjacent sequences: A328690 A328691 A328692 * A328694 A328695 A328696

Keyword

nonn

Author

Andrew Howroyd, Oct 25 2019

Status

approved