|
%I #10 May 31 2022 12:46:13
%S 2,2,6,12,20,6,42,56,72,20,110,12,156,42,30,240,272,72,342,20,42,110,
%T 506,72,600,156,702,56,812,30,930,992,132,272,210,72,1332,342,156,240,
%U 1640,42,1806,132,90,506,2162,240,2352,600,306,156,2756,702,110,56,342,812,3422,240
%N Smallest oblong number m*(m+1) that is divisible by n.
%C Equals A344005(n)*(A344005(n)+1). See A344005 for much more about this problem.
%H Chai Wah Wu, <a href="/A345988/b345988.txt">Table of n, a(n) for n = 1..10000</a>
%o (Python 3.8+)
%o from itertools import combinations
%o from math import prod
%o from sympy import factorint
%o from sympy.ntheory.modular import crt
%o def A345988(n):
%o if n == 1:
%o return 2
%o plist = tuple(p**q for p, q in factorint(n).items())
%o return n*(n-1) if len(plist) == 1 else (s:= int(min(min(crt((m, n//m), (0, -1))[0], crt((n//m, m), (0, -1))[0]) for m in (prod(d) for l in range(1, len(plist)//2+1) for d in combinations(plist, l)))))*(s+1) # _Chai Wah Wu_, May 31 2022
%Y Cf. A002378, A344005.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Jul 13 2021
|
