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

30, 105, 1729, 1105, 13981, 1729, 88537, 50881, 51319, 13981, 137149, 29341, 548497, 88537, 285541, 186337, 3372529, 51319, 18326641, 252601, 1152271, 137149, 1809641, 1366633, 3828001, 548497, 4814857, 645569, 4797703, 285541, 79230049, 4811297

Offset

1,1

Comments

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

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Example

a(1) =  2*3*5 = 30
a(2) =  3*5*7 = 105
a(3) =  7*13*19 = 1729
a(4) =  5*13*17 = 1105
a(5) = 11*31*41 = 13981

Prog

(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

Crossrefs

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

Sequence in context: A257891 A158445 A046301 * A266955 A368565 A205836

Adjacent sequences: A193870 A193871 A193872 * A193874 A193875 A193876

Keyword

nonn,easy

Author

Omar E. Pol, Sep 02 2011

Status

approved