A083954 Least integer coefficients of A(x), where 1<=a(n)<=4, such that A(x)^(1/4) consists entirely of integer coefficients.

1, 4, 2, 4, 3, 4, 4, 4, 1, 4, 4, 4, 3, 4, 4, 4, 3, 4, 4, 4, 2, 4, 2, 4, 4, 4, 4, 4, 3, 4, 2, 4, 2, 4, 2, 4, 3, 4, 2, 4, 3, 4, 2, 4, 4, 4, 2, 4, 2, 4, 4, 4, 2, 4, 4, 4, 2, 4, 2, 4, 1, 4, 4, 4, 1, 4, 2, 4, 4, 4, 4, 4, 1, 4, 2, 4, 3, 4, 4, 4, 4, 4, 4, 4, 3, 4, 4, 4, 2, 4, 2, 4, 2, 4, 2, 4, 1, 4, 4, 4, 1, 4, 2, 4, 3

Offset

0,2

Comments

More generally, "least integer coefficients of A(x), where 1<=a(n)<=m, such that A(x)^(1/m) consists entirely of integer coefficients", appears to have a unique solution for all m>0. Is this sequence periodic?

From M. F. Hasler, Jan 27 2025: (Start)

The sequence does not seem to become periodic.

Positions of '1's are: (0, 8, 60, 64, 72, 96, 100, 112, 116, 148, 160, 176, 184, 200, 240, 248, 268, 288, 304, 328, 336, 360, 376, 380, 384, 400, 408, 420, 424, 448, 460, 472, ...). All seem to be multiples of 4, mostly multiples of 8.

Positions of '3's are: (4, 12, 16, 28, 36, 40, 76, 84, 104, 124, 136, 172, 192, 196, 208, 212, 220, 232, 252, 260, 284, 296, 312, 364, 368, 392, 404, 428, 432, 436, 452, 456, 468, 488, 492, ...). All seem to be (mostly odd) multiples of 4.

The proportions of '1's, '2's, '3's and '4's among the terms are approximately: 6.5%, 18%, 6.5%, 69%. (Roughly the same values for the first 500 or 5000 terms.) (End)

Links

Robert G. Wilson v, Table of n, a(n) for n = 0..5000.

N. Heninger, E. M. Rains and N. J. A. Sloane, On the Integrality of n-th Roots of Generating Functions, arXiv:math/0509316 [math.NT], 2005-2006; J. Combinatorial Theory, Series A, 113 (2006), 1732-1745.

Mathematica

a[0] = 1; a[n_] :=a[n] = Block[{k=1, s = Sum[a[i]*x^i, {i, 0, n-1}]}, While[ Union[ IntegerQ /@ CoefficientList[ Series[(s+k*x^n)^(1/4), {x, 0, n}], x]] != {True}, k++ ]; k]; Table[ a[n], {n, 0, 104}] (* Robert G. Wilson v, Jul 26 2005 *)

Prog

(PARI) A083954_upto(N=99)=vector(N+1, n, if(n>1, for(k=1, 4, denominator(polcoeff(sqrtn(O(x^n)+N+=x^(n-1), 4), n-1))>1|| [n=k, break]); n, N=1)) \\ _M. F. Hasler, Jan 27 2025

Crossrefs

Cf. A083952, A083953, A083945, A083946.

Sequence in context: A056158 A330093 A010316 * A038702 A085062 A053051

Adjacent sequences: A083951 A083952 A083953 * A083955 A083956 A083957

Keyword

nonn

Author

Paul D. Hanna, May 09 2003

Extensions

More terms from Robert G. Wilson v, Jul 26 2005

Status

approved