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 A068808 Triangular numbers with strictly increasing sum of digits. 2
 1, 3, 6, 28, 66, 78, 378, 496, 1596, 5778, 5995, 8778, 47895, 58996, 196878, 468996, 887778, 1788886, 4896885, 5897895, 13999986, 15997996, 38997696, 88877778, 179977878, 189978778, 398988876, 686999778, 1699998895, 5779898886, 9876799878, 38689969878, 39689699896, 67898888778, 89996788896, 299789989975 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS K. D. Bajpai, Table of n, a(n) for n = 1..55 EXAMPLE a(4) = 28 = 7 * (7 + 1) / 2, which is 7th triangular number with sum of digits = 2 + 8 = 10.  a(5) = 66 = 11 * (11 + 1) / 2, which is 11th triangular number with sum of digits = 6 + 6 = 12. Since  12 > 10, 28 and 66 are in list. - K. D. Bajpai, Sep 04 2014 MAPLE dig := X->convert((convert(X, base, 10)), `+`); T := k->k*(k+1)/2; S := k->seq(dig(T(i)), i=1..k-1); seq(`if`(n>1 and dig(T(n))>max(S(n)), T(n), printf("")), n=1..2000); MATHEMATICA t = {}; s = 0; Do[If[(x = Total[IntegerDigits[y = n*(n + 1)/2]]) > s, AppendTo[t, y]; s = x], {n, 120000}]; t (* Jayanta Basu, Aug 06 2013 *) PROG (PARI) tri(n)=n*(n+1)/2; A068808=List; listput(A068808, 1, 1); y=2; for(k=1, 100000, if(sumdigits(Vec(A068808)[y-1])

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Last modified May 26 23:51 EDT 2019. Contains 323597 sequences. (Running on oeis4.)