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A176655
Numbers that are divisible by exactly 7 distinct primes.
10
510510, 570570, 690690, 746130, 870870, 881790, 903210, 930930, 1009470, 1021020, 1067430, 1111110, 1138830, 1141140, 1193010, 1217370, 1231230, 1272810, 1291290, 1345890, 1360590, 1381380, 1385670, 1411410, 1438710
OFFSET
1,1
LINKS
EXAMPLE
1711710 = 2 * 3^2 * 5 * 7 * 11 * 13 * 19.
MATHEMATICA
Select[Range[9!, 5*9! ], Length[FactorInteger[ # ]]==7&]
Select[Range[144*10^4], PrimeNu[#]==7&] (* Harvey P. Dale, Jul 05 2022 *)
PROG
(PARI) isA176655(n)=omega(n)==7 \\ Charles R Greathouse IV, Mar 11 2011
(PARI) (PARI) A246655(lim)=my(v=List(primes([2, lim\=1]))); for(e=2, logint(lim, 2), forprime(p=2, sqrtnint(lim, e), listput(v, p^e))); Set(v)
list(lim, pr=7)=if(pr==1, return(A246655(lim))); my(v=List(), pr1=pr-1, mx=prod(i=1, pr1, prime(i))); forprime(p=prime(pr), lim\mx, my(u=list(lim\p, pr1)); for(i=1, #u, listput(v, p*u[i]))); Set(v) \\ Charles R Greathouse IV, Feb 03 2023
CROSSREFS
Row 7 of A125666.
Sequence in context: A273987 A250057 A230619 * A123321 A258362 A147574
KEYWORD
nonn
AUTHOR
STATUS
approved