A078256 Triangular numbers in which frequency of occurrence of every digit is same.

0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 190, 210, 231, 253, 276, 325, 351, 378, 406, 435, 465, 496, 528, 561, 630, 666, 703, 741, 780, 820, 861, 903, 946, 1035, 1275, 1326, 1378, 1485, 1540, 1596, 1653, 1830, 1953, 2016, 2145

Offset

1,3

Links

Andrew Howroyd, Table of n, a(n) for n = 1..10000

Mathematica

T[n_] := n*(n + 1)/2; f[n_] := Block[{dc = DigitCount[n], s}, s = Select[dc, Positive]; Min @@ s == Max @@ s]; Select[Array[T, 70, 0], f] (* Ray Chandler, May 11 2007 *)

Prog

(PARI) \\ here isok(k) tests if each digit k has equal frequency.
isok(k)={my(f=vector(10)); foreach(digits(k), t, f[1+t]++); my(c=vecmax(f)); 0==#select(t->t>0&&t<c, f)}
lista(n)={my(L=List(), k=0); while(#L<n, my(t=k*(k+1)/2); if(isok(t), listput(L, t)); k++); Vec(L)} \\ Andrew Howroyd, Sep 21 2024

Crossrefs

Cf. A052046, A082646.

Sequence in context: A109811 A025747 A025738 * A025731 A077367 A077366

Adjacent sequences: A078253 A078254 A078255 * A078257 A078258 A078259

Keyword

base,easy,nonn

Author

Amarnath Murthy, Nov 24 2002

Extensions

Offset changed by Andrew Howroyd, Sep 21 2024

Status

approved