This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A077380 Largest n-digit squarefree number whose internal as well as external digits form a squarefree number, or 0 if no such number exists. 5
 0, 0, 977, 9977, 99987, 999987, 9999987, 99999977, 999999985, 9999999987, 99999999987, 999999999987, 9999999999987, 99999999999987, 999999999999987, 9999999999999987, 99999999999999987, 999999999999999987 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS MAPLE with(numtheory) ; A077380 := proc(n) local anmax, leadd, edit, idit ; anmax := 10^n-1 ; while anmax >= 10^(n-1) do leadd := floor(anmax/10^(n-1)) ; edit := 10*leadd + ( anmax mod 10 ); idit := floor(anmax/10) -leadd*10^(n-2) ; if issqrfree(anmax) and issqrfree(edit) and issqrfree(idit) then RETURN(anmax) ; fi ; anmax := anmax-1 ; od ; RETURN(0) ; end: printf("0, ") ; for n from 2 to 30 do printf("%d, ", A077380(n)) ; od ; # R. J. Mathar, Sep 26 2006 CROSSREFS Cf. A077376, A077377, A077378, A077379. Sequence in context: A264130 A282405 A077362 * A063052 A231708 A172158 Adjacent sequences:  A077377 A077378 A077379 * A077381 A077382 A077383 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 06 2002 EXTENSIONS More terms from R. J. Mathar, Sep 26 2006 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.

Last modified December 6 14:15 EST 2019. Contains 329806 sequences. (Running on oeis4.)