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A268516 Take alternate digits of 2^n. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

REFERENCES

GCHQ Director's Christmas Puzzles for 2015.

LINKS

Table of n, a(n) for n=0..43.

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

CROSSREFS

Cf. A000079.

Sequence in context: A133145 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

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Last modified December 18 12:06 EST 2018. Contains 318229 sequences. (Running on oeis4.)