OFFSET
1,1
FORMULA
a(n) ~ A046390(n) ~ A046386(n) ~ A014613(n) ~ 6n log n / (log log n)^3. - Charles R Greathouse IV, Dec 06 2024
EXAMPLE
1155 is a term because 1155=3*5*7*11 is the product of four distinct primes and it is larger than the sum of its proper divisors (1+3+5+7+11+15+21+33+35+55+77+105+165+231+385=1149).
1365 is a term because 1365=3*5*7*13 is the product of four distinct primes and it is larger than the sum of its proper divisors (1+3+5+7+13+15+21+35+39+65+91+105+195+273+455=1323).
MATHEMATICA
q[n_] := Module[{f = FactorInteger[n]}, f[[;; , 2]] == {1, 1, 1, 1} && Times @@ (1 + 1/f[[;; , 1]]) < 2]; Select[Range[6000], q] (* Amiram Eldar, Dec 05 2024 *)
PROG
(PARI) catpr(~v, lim, mult, startAt)=forprime(p=startAt, lim\mult, listput(v, mult*p))
list(lim)=my(v=List()); forprime(p=3, sqrtnint(lim\=1, 4), forprime(q=p+2, sqrtnint(lim\p, 3), forprime(r=q+2, sqrtint(lim\p\q), catpr(~v, lim, p*q*r, r+2)))); forprime(p=11, sqrtnint(lim\2, 3), forprime(q=13, sqrtint(lim\2\p), catpr(~v, lim, 2*p*q, q+2))); forprime(p=13, sqrtint(lim\14), catpr(~v, lim, 14*p, p+2)); forprime(p=19, sqrtint(lim\10), catpr(~v, lim, 10*p, p+2)); catpr(~v, lim, 154, 17); catpr(~v, lim, 110, 59); catpr(~v, lim, 130, 37); catpr(~v, lim, 170, 23); Set(v) \\ Charles R Greathouse IV, Dec 06 2024
CROSSREFS
KEYWORD
nonn,new
AUTHOR
Massimo Kofler, Dec 05 2024
STATUS
approved