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A025721
Index of 7^n within sequence of numbers of form 3^i*7^j for i >= 0, j >= 1.
1
1, 3, 7, 13, 21, 30, 41, 54, 69, 85, 103, 123, 145, 169, 194, 221, 250, 281, 313, 347, 383, 421, 460, 501, 544, 589, 636, 684, 734, 786, 840, 895, 952, 1011, 1072, 1134, 1198, 1264, 1332, 1402, 1473, 1546, 1621, 1698, 1776, 1856, 1938, 2022, 2108, 2195, 2284
OFFSET
1,2
LINKS
EXAMPLE
a(1) = 1, a(2) = 3 and a(3) = 7 because the first 7 numbers of the form 3^i * 7^j with i >= 0 and j >= 1 are 7, 21, 49, 63, 147, 189 and 343. - Robert Israel, Aug 20 2024
MAPLE
dA:= map(t -> 1+ilog[3](7^t), [$0..100]):
ListTools:-PartialSums(dA); # Robert Israel, Aug 20 2024
CROSSREFS
Sequence in context: A299476 A077853 A256588 * A298267 A235532 A195020
KEYWORD
nonn
EXTENSIONS
Name clarified by Robert Israel, Aug 20 2024
STATUS
approved