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 A193873 Smallest product of three distinct primes of the form n*k+1. 3

%I

%S 30,105,1729,1105,13981,1729,88537,50881,51319,13981,137149,29341,

%T 548497,88537,285541,186337,3372529,51319,18326641,252601,1152271,

%U 137149,1809641,1366633,3828001,548497,4814857,645569,4797703,285541,79230049,4811297

%N Smallest product of three distinct primes of the form n*k+1.

%C Note that the Hardy-Ramanujan is the first and the smallest repeated number: a(3)=a(6)=1729.

%H Charles R Greathouse IV, <a href="/A193873/b193873.txt">Table of n, a(n) for n = 1..10000</a>

%e a(1) = 2*3*5 = 30

%e a(2) = 3*5*7 = 105

%e a(3) = 7*13*19 = 1729

%e a(4) = 5*13*17 = 1105

%e a(5) = 11*31*41 = 13981

%o (PARI) a(n)=my(p,q,k=1);while(!isprime(k+=n),);p=k;while(!isprime(k+=n),);q=k;while(!isprime(k+=n),);p*q*k \\ _Charles R Greathouse IV_, Sep 03 2011

%Y Cf. A001235, A077316, A092609, A121940, A154729, A193869.

%K nonn,easy

%O 1,1

%A _Omar E. Pol_, Sep 02 2011

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Last modified July 17 02:47 EDT 2019. Contains 325092 sequences. (Running on oeis4.)