The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A204502 Numbers such that floor[a(n)^2 / 9] is a square. 20
 0, 1, 2, 3, 4, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99, 102, 105, 108, 111, 114, 117, 120, 123, 126, 129, 132, 135, 138, 141, 144, 147, 150, 153, 156, 159, 162, 165, 168, 171, 174, 177 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Or, numbers n such that n^2, with its last base-9 digit dropped, is again a square. (Except maybe for the 3 initial terms whose square has only 1 digit in base 9.) LINKS M. F. Hasler, Truncated squares, OEIS wiki, Jan 16 2012 FORMULA Conjecture: a(n) = 3*n-12 for n>5. G.f.: x^2*(x^2+x+1)*(x^3-x+1)/(x-1)^2. [Colin Barker, Nov 23 2012] MATHEMATICA Select[Range[0, 200], IntegerQ[Sqrt[Floor[#^2/9]]]&] (* Harvey P. Dale, May 05 2018 *) PROG (PARI) b=9; for(n=0, 200, issquare(n^2\b) & print1(n", ")) CROSSREFS The squares are in A204503, the squares with last base-9 digit dropped in A204504, and the square roots of the latter in A028310. Cf. A031149=sqrt(A023110) (base 10), A204514=sqrt(A055872) (base 8), A204516=sqrt(A055859) (base 7), A204518=sqrt(A055851) (base 6), A204520=sqrt(A055812) (base 5), A004275=sqrt(A055808) (base 4), A001075=sqrt(A055793) (base 3), A001541=sqrt(A055792) (base 2). Sequence in context: A128166 A240470 A112249 * A062437 A060729 A229169 Adjacent sequences:  A204499 A204500 A204501 * A204503 A204504 A204505 KEYWORD nonn AUTHOR M. F. Hasler, Jan 15 2012 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 May 18 08:21 EDT 2021. Contains 343995 sequences. (Running on oeis4.)