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 A068616 Starting from a(1)=7, each subsequent term is the minimal square obtained by inserting at least one digit into the previous term. 1
 7, 576, 5476, 54756, 1547536, 154753600, 15475360000, 1547536000000, 154753600000000, 15475360000000000, 1547536000000000000, 154753600000000000000, 15475360000000000000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..13. Index entries for linear recurrences with constant coefficients, signature (100). FORMULA For n>=5, a(n) = 1547536*100^(n-5). From Chai Wah Wu, Aug 03 2020: (Start) a(n) = 100*a(n-1) for n > 5. G.f.: x*(3928064*x^4 + 492844*x^3 + 52124*x^2 + 124*x - 7)/(100*x - 1). (End) EXAMPLE a(2)=576 hence a(3) = 5476 the smallest square formed from 576. MAPLE Digits := 30 : isContain := proc(n, k) local ndigs, kdigs, f, d ; ndigs := convert(n, base, 10) ; kdigs := convert(k, base, 10) ; f := 1 : for d from 1 to nops(ndigs) do if f > nops(kdigs) then RETURN(false) ; fi ; while op(f, kdigs) <> op(d, ndigs) do f := f+1 ; if f > nops(kdigs) then RETURN(false) ; fi ; od: f := f+1 ; od: RETURN(true) ; end: n := 7 ; s := 8 : while true do while not isContain(n, s^2) do s := s+1 : od ; print(s^2) ; n := s^2: s := ceil(sqrt(s^2+1)) : od: # R. J. Mathar, Jun 26 2007 CROSSREFS Cf. A068175, A068176, A068177, A068178. Sequence in context: A159029 A308582 A332157 * A080810 A153405 A322899 Adjacent sequences: A068613 A068614 A068615 * A068617 A068618 A068619 KEYWORD base,nonn AUTHOR Amarnath Murthy, Feb 25 2002 EXTENSIONS More terms from R. J. Mathar, Jun 26 2007 5 more terms from Sean A. Irvine, Sep 27 2009 Edited by Max Alekseyev, Oct 12 2009 STATUS approved

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Last modified December 7 01:49 EST 2023. Contains 367616 sequences. (Running on oeis4.)