A371991 - OEIS

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A371991

Number of different closest packings of equal spheres for hexagonal crystals having repeat period n.

3

1, 1, 0, 1, 1, 2, 3, 6, 6, 16, 21, 42, 63, 129, 201, 404, 685, 1340, 2385, 4625, 8487, 16409, 30735, 59282, 112530, 217182, 415605, 803076, 1545463, 2990945, 5778267, 11201472, 21702645, 42140890, 81830744, 159139428, 309590883, 602935713, 1174779207, 2290915478, 4469734225, 8726815041, 17047041429, 33319598126

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

LINKS

Table of n, a(n) for n=1..44.

J. E. Iglesias, A formula for the number of closest packings of equal spheres having a given repeat period, Z. Krist. 155 (1981) 121-127, Table 1.

FORMULA

a(n) + A371992(n) = A000046(n).

a(n+1)/a(n) = 2 - 2/n + O(1/n^2). - M. F. Hasler, Jun 09 2025

PROG

(PARI) apply( {A371991(n)=A000046(n)-A371992(n)}, [1..40]) \\ M. F. Hasler, Jun 09 2025

CROSSREFS

Cf. A000046, A371992.

Sequence in context: A007894 A102625 A117777 * A223547 A049297 A285664

Adjacent sequences: A371988 A371989 A371990 * A371992 A371993 A371994

KEYWORD

nonn

AUTHOR

R. J. Mathar, Apr 15 2024

EXTENSIONS

Offset changed to 1 and a(1) = 1 prefixed by M. F. Hasler, Jun 09 2025

STATUS

approved