%N a(1) = 1, and for n > 1, a(n) is the least prime power of the form p^k >= n where p is a prime factor of n.
%C This sequence has similarities with A289280.
%C Each power of a prime appears in the sequence.
%C Each prime number appears once in the sequence.
%H Rémy Sigrist, <a href="/A319605/b319605.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) >= n with equality iff n belongs to A000961.
%e For n = 42:
%e - 42 has 3 primes factors: 2, 3 and 7,
%e - the least power of 2 >= 42 is 64,
%e - the least power of 3 >= 42 is 81,
%e - the least power of 7 >= 42 is 49,
%e - hence a(42) = 49.
%o (PARI) a(n) = my (pp=factor(n)[,1]~); if (#pp <= 1, n, vecmin(apply(p -> p^(1+logint(n,p)), pp)))
%Y Cf. A000961, A289280.
%A _Rémy Sigrist_, Jan 07 2019