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A119100 Numbers n such that the n-th triangular number contains only digits {1,2,4}. 2
1, 6, 66, 666, 1686, 2913, 6666, 9406, 15761, 66666, 666666, 6666666, 47140518, 66666666, 206951318, 666666666, 1512753193, 6666666666, 9406509886, 66666666666, 297026066681, 666666666666, 6666666666666, 66666666666666 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

After 0, A002280 is a subsequence because A000217(A002280(m)) = (2*(10^m-1)/9)*10^m + (10^m-1)/9, which provides numbers of the type 22..2211..11 where 2's and 1's are repeated m times. - Bruno Berselli, Feb 24 2016

LINKS

Table of n, a(n) for n=1..24.

G. Resta, Tridigital Triangular Numbers

MATHEMATICA

Select[Range[2 10^7], Complement[IntegerDigits[# (# + 1)/2], {1, 2, 4}] == {} &] (* Vincenzo Librandi, Feb 24 2016 *)

PROG

(MAGMA) [n: n in [1..2*10^7] | Set(Intseq(n*(n+1) div 2)) subset [1, 2, 4]]; // Vincenzo Librandi, Feb 24 2016

CROSSREFS

Cf. A000217, A002280, A119099.

See A119034 for a table of cross-references.

Sequence in context: A156237 A119142 A119091 * A119176 A155630 A119125

Adjacent sequences:  A119097 A119098 A119099 * A119101 A119102 A119103

KEYWORD

nonn,base

AUTHOR

Giovanni Resta, May 10 2006

STATUS

approved

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Last modified September 28 07:54 EDT 2020. Contains 337394 sequences. (Running on oeis4.)