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A173172
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Numbers n such that sopf(n) divides sopf(n+1) and sopf(n+1) divides sopf(n+2).
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1
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24, 225504, 944108, 10869375, 11506989, 12792675, 20962395, 25457760, 79509528, 89002914, 89460294, 146767704, 161064864, 180173147, 219487320, 235762488, 252508509, 419785344, 434887029, 453160511, 487179000, 545112792, 813133607
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OFFSET
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1,1
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COMMENTS
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The sum of the distinct primes dividing n (without repetition) is sometimes called sopf(n).
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REFERENCES
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M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 844.
T. M. Apostol, Introduction to Analytic Number Theory, Springer-Verlag, 1976, page 38.
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 225504, p. 264, Ellipses, Paris 2008.
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LINKS
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EXAMPLE
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sopf(24) = 5, sopf(25) = 5, sopf(26) = 15; and 5 divides 5, 5 and divides 15.
sopf(225504) = 34, sopf(225505) = 408, sopf(225506) = 2448; and 34 divides 408, and 408 divides 2448.
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MAPLE
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with(numtheory): for n from 2 to 100000000 do : t1 := ifactors(n)[2] : t2 := sum(t1[i][1], i=1..nops(t1)) : tt1 :=ifactors(n+1)[2] :tt2 := sum(tt1[i][1], i=1..nops(tt1)): ttt1:=ifactors(n+2)[2] : ttt2 := sum(ttt1[i][1], i=1..nops(ttt1)): a:= tt2/t2 ; aa:=floor(a) ; b := ttt2/tt2:bb:=floor(b): if a=aa and b=bb then print (n): else fi: od:
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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