OFFSET
1,1
COMMENTS
Members of A135581, sorted. Characterizations (see Formulas section, below) are possible for similar sequences as well.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
FORMULA
Characterization: all terms of this sequence are of the form p, p^3, p^4, or pq where p and q are distinct primes. All but 16 primes {2, 3, 5, 7, 17, 19, 23, 83, 89, 97, 101, 103, 107, 109, 113} are in this sequence; all p^3 and p^4 are in this sequence; pq is in this sequence for all p < q < p^2.
PROG
(PARI) is(n)=my(f=factor(n)); if(#f[, 1]==1, f[1, 2]==3||f[1, 2]==4||(f[1, 2]==1&&(f[1, 1]>126||(f[1, 1]<80&&f[1, 1]>28)||f[1, 1]==11||f[1, 1]==13)), #f[, 1]==2&&f[1, 2]==1&&f[2, 2]==1&&f[2, 1]<f[1, 1]^2)
CROSSREFS
KEYWORD
nonn
AUTHOR
Charles R Greathouse IV, Nov 29 2011
STATUS
approved