A028363 Total number of doubly-even self-dual binary codes of length 8n.

1, 30, 9845550, 171634285407048750, 193419995622362136809061156168750, 14272693289804307141953423466197932293533748208968750

Offset

0,2

References

F. J. MacWilliams and N. J. A. Sloane, The Theory of Error-Correcting Codes, Elsevier-North Holland, 1978, p. 631.

Links

Table of n, a(n) for n=0..5.

Formula

a(n) = 2*Product_{i=1..4n-2} (2^i + 1).

Mathematica

Join[{1}, Table[2*Product[2^i+1, {i, 4n-2}], {n, 6}]] (* Harvey P. Dale, May 08 2013 *)
Table[Product[2^i + 1, {i, 0, n/2 - 2}], {n, 8, 40, 8}] (* Nathan J. Russell, Mar 04 2016 *)

Prog

(Python)
for n in range(8, 50, 8):
    product = 1
    for i in range(n//2 - 1):
        product *= 2**i + 1
    print(product, end=", ")
# Nathan J. Russell, Mar 01 2016

Crossrefs

Cf. A003178, A003179, A028362.

Sequence in context: A238636 A373502 A140762 * A091511 A324684 A213070

Adjacent sequences: A028360 A028361 A028362 * A028364 A028365 A028366

Keyword

nonn,easy,nice

Author

N. J. A. Sloane

Extensions

There is an error in Eq. (75) of F. J. MacWilliams and N. J. A. Sloane, the lower subscript should be 1 not 0.

Formula corrected by N. J. A. Sloane, May 07 2013 following a suggestion from Harvey P. Dale

Status

approved