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Index of 7^n within sequence of numbers of form 2^i*7^j.
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%I #5 Mar 30 2012 18:35:26

%S 1,4,10,19,31,46,63,83,106,132,161,192,226,263,303,346,391,439,490,

%T 544,601,660,722,787,855,926,999,1075,1154,1236,1321,1409,1499,1592,

%U 1688,1787,1889,1993,2100,2210,2323,2439,2557,2678,2802,2929,3059,3191,3326

%N Index of 7^n within sequence of numbers of form 2^i*7^j.

%K nonn

%O 1,2

%A _David W. Wilson_