cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A346393 Irregular triangle read by rows: the n-th row gives the divisors of n ending with the final digit of n.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 11, 2, 12, 13, 14, 5, 15, 16, 17, 18, 19, 10, 20, 1, 21, 2, 22, 23, 4, 24, 5, 25, 26, 27, 28, 29, 10, 30, 1, 31, 2, 32, 3, 33, 34, 5, 35, 6, 36, 37, 38, 39, 10, 20, 40, 1, 41, 2, 42, 43, 4, 44, 5, 15, 45, 46, 47, 8, 48, 49, 10, 50
Offset: 1

Views

Author

Stefano Spezia, Jul 21 2021

Keywords

Examples

			The triangle begins:
    1
    2
    3
    4
    5
    6
    7
    8
    9
   10
    1     11
    2     12
   13
   14
    5     15
   16
   17
   18
   19
   10     20
    1     21
    2     22
   23
    4     24
    5     25
   26
   27
   28
   29
   10     30
    1     31
    2     32
    3     33
   34
    5     35
    6     36
   37
   38
   39
   10     20     40
   ...
		

Crossrefs

Cf. A010879, A027750, A330348 (row length).

Programs

  • Mathematica
    r[n_]:=Drop[Select[Divisors[n],(Mod[#,10]==Mod[n,10]&)]]; Flatten[Array[r, 50]]
  • PARI
    row(n) = select(x->(x%10) == (n%10), divisors(n)); \\ Michel Marcus, Jul 25 2021
  • Python
    from sympy import divisors
    def auptorow(nn):
        for n in range(1, nn+1):
            yield from [d for d in divisors(n) if d%10 == n%10]
    print([an for an in auptorow(50)]) # Michael S. Branicky, Jul 21 2021