A117304 Numbers with an even number of digits such that the second half is twice the first half.

12, 24, 36, 48, 1020, 1122, 1224, 1326, 1428, 1530, 1632, 1734, 1836, 1938, 2040, 2142, 2244, 2346, 2448, 2550, 2652, 2754, 2856, 2958, 3060, 3162, 3264, 3366, 3468, 3570, 3672, 3774, 3876, 3978, 4080, 4182, 4284, 4386, 4488, 4590, 4692, 4794, 4896

Offset

1,1

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000

Example

1020 is in the sequence because 20 = 2*10.

Prog

(Python)
from itertools import count, islice, takewhile
def agen():
    for d in count(2, 2):
        t = (int(str(k) + str(2*k)) for k in count(10**(d//2-1)))
        yield from takewhile(lambda x: x < 10**d, t)
print(list(islice(agen(), 43))) # Michael S. Branicky, Dec 24 2021

Crossrefs

Subsequence of A019550.

Sequence in context: A358693 A371413 A019550 * A022759 A335540 A091193

Adjacent sequences: A117301 A117302 A117303 * A117305 A117306 A117307

Keyword

nonn,base,easy

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 26 2006

Status

approved