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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The corresponding indices of a(n) in A246655 are 1, 3, 12, 240, ... LINKS Table of n, a(n) for n=0..4. 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 Adjacent sequences: A332988 A332989 A332990 * A332992 A332993 A332994 KEYWORD nonn,hard,more AUTHOR Ilya Gutkovskiy, Mar 05 2020 EXTENSIONS a(4) from Daniel Suteu, Mar 05 2020 STATUS approved

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Last modified September 7 21:14 EDT 2024. Contains 375749 sequences. (Running on oeis4.)