A025612 Numbers of form 2^i*10^j, with i, j >= 0.

1, 2, 4, 8, 10, 16, 20, 32, 40, 64, 80, 100, 128, 160, 200, 256, 320, 400, 512, 640, 800, 1000, 1024, 1280, 1600, 2000, 2048, 2560, 3200, 4000, 4096, 5120, 6400, 8000, 8192, 10000, 10240, 12800, 16000, 16384, 20000, 20480, 25600, 32000, 32768, 40000, 40960

Offset: 1

Author

David W. Wilson

Keywords

• easy
• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A000079 and A011557.

Subsequences: A025621 and A025634.

Programs

Mathematica

n = 10^5; Flatten[Table[2^i*10^j, {i, 0, Log2[n]}, {j, 0, Log10[n/2^i]}]] // Sort (* Amiram Eldar, Sep 25 2020 *)

PARI

list(lim)=my(v=List(), N); for(n=0, logint(lim\=1, 10), N=10^n; while(N<=lim, listput(v, N); N<<=1)); Set(v) \\ Charles R Greathouse IV, Jan 10 2018

Formula

Sum_{n>=1} 1/a(n) = (2*10)/((2-1)*(10-1)) = 20/9. - Amiram Eldar, Sep 25 2020

a(n) ~ exp(sqrt(2*log(2)*log(10)*n)) / sqrt(20). - Vaclav Kotesovec, Sep 25 2020

a(n) = 2^A025639(n) * 10^A025684(n). - R. J. Mathar, Jul 06 2025