A392217 Irregular triangle read by rows: the n-th row gives the divisors of phi(n).

1, 1, 1, 2, 1, 2, 1, 2, 4, 1, 2, 1, 2, 3, 6, 1, 2, 4, 1, 2, 3, 6, 1, 2, 4, 1, 2, 5, 10, 1, 2, 4, 1, 2, 3, 4, 6, 12, 1, 2, 3, 6, 1, 2, 4, 8, 1, 2, 4, 8, 1, 2, 4, 8, 16, 1, 2, 3, 6, 1, 2, 3, 6, 9, 18, 1, 2, 4, 8, 1, 2, 3, 4, 6, 12, 1, 2, 5, 10, 1, 2, 11, 22, 1, 2, 4, 8, 1, 2, 4, 5, 10, 20

Offset

1,4

Links

Stefano Spezia, Table of n, a(n) for n = 1..13241 (first 1000 rows of the triangle)

Index entries for sequences related to divisors of numbers.

Example

The irregular triangle begins as:
  1;
  1;
  1, 2;
  1, 2;
  1, 2, 4;
  1, 2;
  1, 2, 3,  6;
  1, 2, 4;
  1, 2, 3,  6;
  1, 2, 4;
  1, 2, 5, 10;
  1, 2, 4;
  1, 2, 3,  4, 6, 12;
  ...

Mathematica

row[n_]:=Divisors[EulerPhi[n]]; Array[row, 25]//Flatten

Crossrefs

Cf. A000010, A000012 (1st column), A027750, A062402 (row sums), A392218 (row products).

Sequence in context: A182063 A135990 A347256 * A347224 A339270 A345226

Adjacent sequences: A392214 A392215 A392216 * A392218 A392219 A392220

Keyword

nonn,easy,look,tabf

Author

Stefano Spezia, Jan 03 2026

Status

approved