A268516 Take alternate digits of 2^n.

1, 2, 4, 8, 1, 3, 6, 18, 26, 52, 12, 24, 49, 89, 134, 378, 656, 117, 224, 548, 1456, 2912, 4934, 8868, 1771, 3543, 6186, 14178, 28346, 56792, 17712, 24434, 49979, 88949, 119614, 339338, 679776, 173937, 247964, 595838, 1951276, 2903552, 4906114, 8903228

Offset

0,2

References

GCHQ Director's Christmas Puzzles for 2015.

Links

Michael S. Branicky, Table of n, a(n) for n = 0..6643

GCHQ, Solutions to Director's Christmas Puzzles for 2015

Example

2^10 = 1024, so a(10) = 12 (omitting the 2nd and 4th digits).

Maple

a:= n-> (s-> parse(cat(seq(s[2*i+1],
    i=0..(length(s)-1)/2))))(""||(2^n)):
seq(a(n), n=0..50);  # Alois P. Heinz, Feb 08 2016

Prog

(PARI) a(n) = my(d = digits(2^n)); my(db = vector(ceil(#d/2), k, Str(d[2*k-1]))); eval(concat(db)); \\ Michel Marcus, Feb 08 2016
(Python)
def a(n): return int(str(2**n)[::2])
print([a(n) for n in range(44)]) # Michael S. Branicky, Dec 25 2021

Crossrefs

Cf. A000079.

Sequence in context: A350208 A317414 A008952 * A021407 A131609 A210022

Adjacent sequences: A268513 A268514 A268515 * A268517 A268518 A268519

Keyword

nonn,base

Author

N. J. A. Sloane, Feb 08 2016

Extensions

More terms from Michel Marcus, Feb 08 2016

Status

approved