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

Author

Amarnath Murthy, Nov 24 2002

Keywords

• base
• easy
• nonn

Links

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

Crossrefs

Cf. A052046, A082646.

Programs

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 *)

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&&tAndrew Howroyd, Sep 21 2024

Extensions

Offset changed by Andrew Howroyd, Sep 21 2024