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A109745
Admirable numbers that set a new record for largest subtracted divisor.
1
12, 24, 84, 120, 270, 672, 1488, 1638, 6200, 24384, 174592, 523776, 44736512, 91963648, 100651008, 459818240, 1476304896, 10200236032, 25769607168, 51001180160, 412316073984
OFFSET
1,1
COMMENTS
The records set are A000203(a(n))/2 - a(n) = 2, 6, 28, 60, 90, 336, 496, 546, 1240, 8128, 21824,... - R. J. Mathar, Feb 12 2008
MATHEMATICA
admDiv[n_] := Module[{ab = DivisorSigma[1, n] - 2*n}, If[ab > 0 && EvenQ[ab] && ab/2 < n && Divisible[n, ab/2], ab/2, 0]];
seq[nmax_] := Module[{dmax = 0, s = {}, d}, Do[d = admDiv[n]; If[d > dmax, dmax = d; AppendTo[s, n]], {n, 1, nmax}]; s]; seq[6*10^5] (* Amiram Eldar, Aug 05 2023 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jason Earls, Aug 10 2005
EXTENSIONS
a(13)-a(20) from Donovan Johnson, Nov 11 2008
a(21) from Amiram Eldar, Aug 05 2023
STATUS
approved