A236372 - OEIS

%I #29 Feb 16 2025 08:33:21

%S 28,200,936,7856640,12103000,8004519424

%N Terms of A050973 that give minimum record values for A050973(k)/A050972(k).

%C The corresponding terms in A050972 are: 6, 80, 864, 7344000, 11804800, 7908221230.

%C Note that from n=1 to 4 sigma(a(n))/a(n) is increasing, but decreasing for n=5 and 6. Is this going on afterwards? - _Michel Marcus_, Feb 08 2014

%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FriendlyPair.html">Friendly Pair</a>.

%e 28/6 > 200/80 > 936/864 > 7856640/7344000 > 12103000/11804800 > ...

%o (PARI) isrmin(i, rmin) = {si = sigma(i); if (gcd(si, i) == 1, return (0)); s = si/i; forstep (j=i-1, 1+i\rmin, -1, if ((sigma(j)/j) == s, if ((newr = i/j) < rmin, return (newr)););); return (0);}

%o lista(nn) = {rmin = 1000; for (i=1, nn, if ((newr = isrmin(i, rmin)), rmin = newr; print1(i, ", ");););}

%Y Cf. A050972, A050973, A236355.

%K nonn,more

%O 1,1

%A _Michel Marcus_, Jan 24 2014

%E a(6) from _Michel Marcus_, Feb 08 2014