A062859 Size of smallest triangular multiplication table which contains some number n times.

1, 4, 12, 18, 30, 40, 60, 72, 90, 120, 140, 168, 180, 210, 252, 280, 315, 336, 360, 420, 504, 560, 630, 672, 720, 792, 840, 924, 990, 1008, 1155, 1232, 1260, 1320, 1386, 1540, 1584, 1680, 1848, 1980, 2016, 2310, 2376, 2520, 2640, 2772, 2970, 3024, 3080

Offset: 1

Author

Ron A. Lalonde (ronronronlalonde(AT)hotmail.com), Jun 25 2001

Keywords

• nonn

Examples

			a(4)=18 because the size-18 triangular multiplication table is the smallest to contain a particular number 4 times (namely the number A062858(4)=36).
		

Crossrefs

The least such number is A062858(n).

Cf. A027424, A062851, A062854, A062855, A062856, A062857, A062858, A000217.

Programs

Python

from itertools import count
from collections import Counter
def A062859(n):
    c = Counter()
    for m in count(1):
        for i in range(1,m+1):
            ij = i*m
            c[ij] += 1
            if c[ij]>=n:
                return m # Chai Wah Wu, Oct 16 2023

Extensions

More terms from Don Reble, Nov 08 2001