login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A068520 Numbers n which can be transformed into a true arithmetic statement by inserting zero or more parentheses and elementary arithmetic operators ((, ), +, -, *, /) and one equality sign (=) as the rightmost insertion into the decimal representation of n. 0

%I

%S 11,22,33,44,55,66,77,88,99,100,101,110,111,112,122,123,133,134,144,

%T 145,155,156,166,167,177,178,188,189,199,200,202,212,213,220,221,224,

%U 235,236,246,248,257,268,279,300,303,312,313,314,321,325,326,330,331

%N Numbers n which can be transformed into a true arithmetic statement by inserting zero or more parentheses and elementary arithmetic operators ((, ), +, -, *, /) and one equality sign (=) as the rightmost insertion into the decimal representation of n.

%C The minus sign is considered only as two-place infix operator, not as one-place prefix operator. Therefore -1 + 2 = 1 is not allowed and 121 is not a term.

%C For obvious reasons these numbers are called (elementary) "didactic numbers".

%H <a href="/index/Fo#4x4">Index entries for similar sequences</a>

%e 7 = 7; 1 * 0 = 0; 2 - 2 = 0; 2 / 2 = 1; 18 / 2 = 9; 2 * (3 + 4) = 14. Therefore 77, 100, 220, 221, 1829 and 23414 are terms of the sequence.

%K base,nonn

%O 1,1

%A _Joseph L. Pe_, Mar 21 2002

%E More terms from Larry Reeves (larryr(AT)acm.org), Jun 21 2002

%E Edited by _Klaus Brockhaus_, Jul 02 2003

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 February 16 21:59 EST 2019. Contains 320200 sequences. (Running on oeis4.)