%N If n = a + 10 * b + 100 * c + 1000 * d + ... then a(n) = (2^a) * (3^b) * (5^c) * (7^d) * ...
%C 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
%C 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
%H R. Zumkeller, <a href="/A054842/b054842.txt">Table of n, a(n) for n = 0..9999</a>
%F 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
%e a(15)=96 because 3^1 * 2^5 = 3*32 = 96.
%o a054842 = f a000040_list 1 where
%o f _ y 0 = y
%o f (p:ps) y x = f ps (y * p ^ d) x' where (x', d) = divMod x 10
%o -- _Reinhard Zumkeller_, Aug 03 2015
%Y Cf. A054841, A085840.
%Y Cf. A019565, A101278. - _Reinhard Zumkeller_, Mar 13 2010
%A _Henry Bottomley_, Apr 11 2000