login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A053318 a(n) contains n digits (either '2' or '7') and is divisible by 2^n. 3
2, 72, 272, 2272, 22272, 222272, 7222272, 27222272, 727222272, 2727222272, 72727222272, 772727222272, 7772727222272, 77772727222272, 277772727222272, 2277772727222272, 72277772727222272, 272277772727222272 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..999

FORMULA

a(n) = a(n-1) + 10^(n-1)*(2 + 5*(a(n-1)/2^(n-1) mod 2)), i.e., a(n) ends with a(n-1); if a(n-1) is divisible by 2^n then a(n) begins with a 2, if not then a(n) begins with a 7.

MAPLE

A[1]:= 2:

for n from 2 to 100 do

   if A[n-1] mod 2^n = 0 then A[n]:= A[n-1]+2*10^(n-1)

   else A[n]:= A[n-1]+7*10^(n-1)

     fi

od:

seq(A[i], i=1..100); # Robert Israel, Oct 27 2019

CROSSREFS

Cf. A023399, A050621, A050622, A035014.

Sequence in context: A055030 A185120 A217842 * A272757 A187707 A163274

Adjacent sequences:  A053315 A053316 A053317 * A053319 A053320 A053321

KEYWORD

base,nonn

AUTHOR

Henry Bottomley, Mar 06 2000

EXTENSIONS

Formula corrected by Robert Israel, Oct 27 2019

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 20 23:29 EST 2020. Contains 331104 sequences. (Running on oeis4.)