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Number of increasing geometric progressions ending in n (in the positive integers), excluding those of length 1 or 2.
2

%I #7 Nov 20 2017 23:42:38

%S 0,0,0,1,0,0,0,2,2,0,0,1,0,0,0,5,0,2,0,1,0,0,0,2,4,0,4,1,0,0,0,6,0,0,

%T 0,5,0,0,0,2,0,0,0,1,2,0,0,5,6,4,0,1,0,4,0,2,0,0,0,1,0,0,2,13,0,0,0,1,

%U 0,0,0,6,0,0,4,1,0,0,0,5,12,0,0,1,0,0,0,2,0,2,0,1,0,0,0,6,0,6,2,9,0,0,0

%N Number of increasing geometric progressions ending in n (in the positive integers), excluding those of length 1 or 2.

%H Antti Karttunen, <a href="/A058190/b058190.txt">Table of n, a(n) for n = 1..16384</a>

%F a(n) = A058189(n) - n.

%e a(16) = 5 since the possibilities are (1,4,16), (1,2,4,8,16), (2,4,8,16), (4,8,16), (9,12,16).

%o (PARI)

%o ends_max_progression_of_length(n,ratio) = { my(k=1); while(1,if(denominator(n)>1,return(k)); n *= ratio; k++;) };

%o A058190(n) = sum(d=1,(n-1),max(0,ends_max_progression_of_length(d,d/n)-2)); \\ _Antti Karttunen_, Nov 19 2017

%Y Cf. A058189.

%K nonn

%O 1,8

%A _Henry Bottomley_, Nov 22 2000