OFFSET
1,1
COMMENTS
Union of {4}, numbers of the form 3^3 * 2^k (k >= 0), and the sequence of sets of numbers of the form p^p * k, where k is a p-smooth number (number not divisible by any prime > p), for primes p >= 3.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = Sum_{k>=1} 1/(prime(k)^prime(k) * Product_{i=1..k-1} (1 - 1/prime(i))) = 0.32503862758571995411... .
MATHEMATICA
Select[Range[2, 10^6], Equal @@ FactorInteger[#][[-1, ;; ]] &]
PROG
(PARI) is(n)={my(f = factor(n), m = #f~); n > 1 && f[m, 1] == f[m, 2]; }
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Feb 20 2024
STATUS
approved