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A176655 Numbers that are divisible by exactly 7 distinct primes. 13
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 (list; graph; refs; listen; history; text; internal format)
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
Numbers divisible by d distinct primes: A246655 (d=1), A007774 (d=2), A033992 (d=3), A033993 (d=4), A051270 (d=5), A074969 (d=6), A176655 (d=7), A348072 (d=8), A348073 (d=9).
Sequence in context: A273987 A250057 A230619 * A123321 A258362 A147574
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified June 10 03:15 EDT 2023. Contains 363186 sequences. (Running on oeis4.)