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A054842 If n = a + 10 * b + 100 * c + 1000 * d + ... then a(n) = (2^a) * (3^b) * (5^c) * (7^d) * ... 14
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 3, 6, 12, 24, 48, 96, 192, 384, 768, 1536, 9, 18, 36, 72, 144, 288, 576, 1152, 2304, 4608, 27, 54, 108, 216, 432, 864, 1728, 3456, 6912, 13824, 81, 162, 324, 648, 1296, 2592, 5184, 10368, 20736, 41472, 243, 486, 972 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
a((10^k-1)/9) = Primorial(k)= A061509((10^k-1)/9). This is a rearrangement of whole numbers. a(m) = a(n) iff m = n. (Unlike A061509, in which a(n) = a(n*10^k)).) - Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jul 14 2003
Part of the previous comment is incorrect: as a set, this sequence consists of numbers n such that the largest exponent appearing in the prime factorization of n is 9. So this cannot be a rearrangement (or permutation) of the natural numbers. - Tom Edgar, Oct 20 2015
LINKS
FORMULA
a(n) = f(n, 1, 1) with f(x, y, z) = if x > 0 then f(floor(x/10), y*prime(z)^(x mod 10), z+1) else y. - Reinhard Zumkeller, Mar 13 2010
EXAMPLE
a(15)=96 because 3^1 * 2^5 = 3*32 = 96.
PROG
(Haskell)
a054842 = f a000040_list 1 where
f _ y 0 = y
f (p:ps) y x = f ps (y * p ^ d) x' where (x', d) = divMod x 10
-- Reinhard Zumkeller, Aug 03 2015
CROSSREFS
Cf. A019565, A101278. - Reinhard Zumkeller, Mar 13 2010
Sequence in context: A086066 A263327 A085941 * A290389 A101440 A126605
KEYWORD
base,nonn,look
AUTHOR
Henry Bottomley, Apr 11 2000
STATUS
approved

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Last modified March 1 22:23 EST 2024. Contains 370443 sequences. (Running on oeis4.)