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

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

1,2

Links

Stefano Spezia, First 5000 rows of the triangle, flattened

Example

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
   ...

Mathematica

r[n_]:=Drop[Select[Divisors[n], (Mod[#, 10]==Mod[n, 10]&)]]; Flatten[Array[r, 50]]

Prog

(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
(PARI) row(n) = select(x->(x%10) == (n%10), divisors(n)); \\ Michel Marcus, Jul 25 2021

Crossrefs

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

Sequence in context: A214949 A067453 A203814 * A360074 A280505 A262401

Adjacent sequences: A346390 A346391 A346392 * A346394 A346395 A346396

Keyword

nonn,tabf,base

Author

Stefano Spezia, Jul 21 2021

Status

approved