OFFSET
1,4
COMMENTS
The sorted sequence of (nonzero) exponents in the prime factorization of a number is called its prime signature. Here this is "approximated" by multiplying them by powers of 10. Up to 2^10 this coincides with the concatenation of these exponents written in base 10 (but that sequence would be "base" specific).
For n >= 1024 one should use a modified definition, replacing 10 with 10^floor(1+log_10(log_2(n))), to avoid ambiguity of the representation.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..1023
Eric Weisstein's World of Mathematics, Prime Signature.
Wikipedia, Prime signature.
PROG
(PARI) A139393(n)=sum(i=1, #n=vecsort(factor(n)[, 2]), 10^(#n-i)*n[i])
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
M. F. Hasler, Apr 17 2008, Apr 19 2008
STATUS
approved