A176655 Numbers that are divisible by exactly 7 distinct primes.

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

Amiram Eldar, Table of n, a(n) for n = 1..10000

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.

Cf. A046386, A046387, A067885, A123321.

Sequence in context: A273987 A250057 A230619 * A123321 A258362 A147574

Adjacent sequences: A176652 A176653 A176654 * A176656 A176657 A176658

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Apr 22 2010

Status

approved