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 A303809 Multiplicative with a(p^k) = 2^a(k). 3
 1, 2, 2, 4, 2, 4, 2, 4, 4, 4, 2, 8, 2, 4, 4, 16, 2, 8, 2, 8, 4, 4, 2, 8, 4, 4, 4, 8, 2, 8, 2, 4, 4, 4, 4, 16, 2, 4, 4, 8, 2, 8, 2, 8, 8, 4, 2, 32, 4, 8, 4, 8, 2, 8, 4, 8, 4, 4, 2, 16, 2, 4, 8, 16, 4, 8, 2, 8, 4, 8, 2, 16, 2, 4, 8, 8, 4, 8, 2, 32, 16, 4, 2, 16 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This sequence contains every power of 2; see A303819 for the corresponding least indices. For any n > 0, a(n) only depends on the prime signature of n. LINKS Rémy Sigrist, Table of n, a(n) for n = 1..10000 FORMULA a(n) <= n with equality iff n = A014221(k) for some k >= 0. a(A002110(k)) = 2^k for any k >= 0. a(n) = 2 iff n is prime. PROG (PARI) a(n) = my (f=factor(n)); prod (i=1, #f~, 2^a(f[i, 2])) CROSSREFS Cf. A002110, A014221, A061142, A303819. Sequence in context: A040003 A106469 A082508 * A193562 A249868 A255311 Adjacent sequences:  A303806 A303807 A303808 * A303810 A303811 A303812 KEYWORD nonn,easy,mult AUTHOR Rémy Sigrist, Apr 30 2018 STATUS approved

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Last modified February 16 14:47 EST 2019. Contains 320163 sequences. (Running on oeis4.)