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A332991
a(n) is the smallest prime power p^k (p prime, k >= 1) such that sum of reciprocals of prime powers up to p^k (prime power harmonic sum) exceeds n.
1
2, 4, 19, 1307, 266655247
OFFSET
0,1
COMMENTS
The corresponding indices of a(n) in A246655 are 1, 3, 12, 240, ...
LINKS
Eric Weisstein's World of Mathematics, Prime Power
EXAMPLE
a(1) = 4 because 1/2 + 1/3 = 0.8333... < 1 but 1/2 + 1/3 + 1/4 = 1.0833... > 1.
CROSSREFS
Similar sequences: A002387 (for positive integers), A016088 (for primes), A076751 (for composite numbers), A333004 (for squarefree numbers).
Cf. A246655 (prime powers).
Sequence in context: A048774 A061213 A063458 * A132530 A316389 A133521
KEYWORD
nonn,hard,more
AUTHOR
Ilya Gutkovskiy, Mar 05 2020
EXTENSIONS
a(4) from Daniel Suteu, Mar 05 2020
STATUS
approved