A233267 a(n) = A055881(A001110(n)); the largest m such that m! divides the n-th positive number which is both triangular and square.

1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1, 11, 1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 4, 1, 3, 1

Offset: 1

Author

Antti Karttunen, Dec 06 2013

Keywords

• nonn

Comments

The sequence seems to have a nice symmetric fractal structure. The new distinct values (records) occur at positions k = 1, 2, 4, 12, 48, 288, 2016, 4032, ... those values being 1, 3, 4, 7, 11, 12, 13, 14, ...

Furthermore, each prefix from 1 to 2*k-1 (centered on a new record) seems to be palindromic. 2*k-1 runs as: 1, 3, 7, 23, 95, 575, 4031, 8063, ...

On the other hand, if we list ALL the positions p where prefix 1..p is palindromic, we obtain a sequence: 1, 3, 7, 11, 23, 35, 47, 95, 143, 191, 239, 287, 575, 863, 1151, 1439, 1727, 2015, 4031, ...

Its first differences is again familiar: 2, 4, 4, 12, 12, 12, 48, 48, 48, 48, 48, 288, 288, 288, 288, 288, 288, 2016, ... which appear to consist of 1, 2, 3, 5, 6, ... copies of the first mentioned sequence from its term 2 onward.

None of these sequences (except maybe the last) are in the OEIS as of Dec 06 2013.

Note: A233269(n) = A055881(A001109(n)) seems to have the same overall structure, but some of the records are missing/different.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..8063

Crossrefs

Cf. A001110, A055881, A233269, A232096-A232098, A233285.

Programs

Scheme

(define (A233267 n) (A055881 (A001110 n)))

Formula

a(n) = A055881(A001110(n)).