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A119160 Triangular numbers composed of digits {2,4,6}. 2
6, 66, 666, 426426, 266262426, 22464262666, 46624464466426, 644644226644644222426, 46424226426466426446424262644446, 626644642222466644646226466422666 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Next term must be greater than 10^37.

All terms end in 6. - Robert Israel, Feb 05 2016

LINKS

Table of n, a(n) for n=1..10.

G. Resta, Tridigital Triangular Numbers

MAPLE

F:= proc(d) # get all terms with d digits

local res, m, prefs, i, t, qmax, qmin, smax, smin, cand, s;

  res:= NULL;

  m:= max(1, floor(d/2-1));

  prefs:= [2, 4, 6]*10^(d-1);

  for i from 1 to m-1 do

    prefs:= map(t -> (t + 2*10^(d-1-i), t+4*10^(d-1-i), t+6*10^(d-1-i)), prefs)

  od;

  for t in prefs do

       qmax:= t + 6*(10^(d-m)-1)/9; smax:= floor(sqrt(8*qmax+1));

       qmin:= t + 2*(10^(d-m)-1)/9; smin:= ceil(sqrt(8*qmin+1));

       smin:= smin + 1 - (smin mod 2);

       for s from smin to smax by 2 do

           cand:= (s^2 -1)/8;

           if cand mod 10 = 6 and convert(convert(cand, base, 10), set) subset {2, 4, 6} then

              res:= res, cand;

           fi

       od

  od;

res;

end proc:

seq(F(d), d=1..21);  # Robert Israel, Feb 05 2016

MATHEMATICA

Select[#*(# + 1)/2 & /@

  Range[1000000], !

MemberQ[IntegerDigits[#], 0 | 1 | 3 | 5 | 7 | 8 | 9] &] (*Julien Kluge, Feb 01 2016*)

PROG

(MAGMA) [t: n in [1..2*10^7] | Set(Intseq(t)) subset {2, 4, 6} where t is n*(n+1) div 2]; // Vincenzo Librandi, Feb 04 2016

CROSSREFS

Cf. A000217, A053923, A119161. See A119033 for a table of cross-references.

Sequence in context: A119089 A036523 A112902 * A119210 A227220 A119234

Adjacent sequences:  A119157 A119158 A119159 * A119161 A119162 A119163

KEYWORD

nonn,base,more

AUTHOR

Giovanni Resta, May 10 2006

EXTENSIONS

a(10) from Max Alekseyev, Jun 16 2011

STATUS

approved

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Last modified November 17 08:39 EST 2019. Contains 329217 sequences. (Running on oeis4.)