A346138 - OEIS

%I #23 Aug 17 2021 07:29:58

%S 651,2667,11811,27559,172011,761763,1777447,2752491,3120771,7281799,

%T 11010027,12189603,28442407,32247967,48758691,49938051,113770279,

%U 116522119,199753347,466091143,516026527,2064117919,3220807683,7515217927,12883304451,30061043719,33281679391,45097156587,133127479327

%N Sphenic numbers that are the product of Mersenne primes.

%C The largest known sphenic number is a term of this sequence.

%C a(n) == 3 (mod 4) for n >= 1.

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Sphenic_number">Sphenic number</a> (lists the largest known sphenic number)

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Mersenne_prime">Mersenne prime</a>

%H <a href="/index/Pri#prime_signature">Index to sequences related to prime signature</a>

%e a(1) = 651, since 651 = 3*7*31.

%e a(2) = 2667, since 2667 = 3*7*127.

%e a(3) = 11811, since 11811 = 3*31*127.

%t M = 2^MersennePrimeExponent[Range[12]] - 1; Take[ Union[ Times @@@ Subsets[ M, {3}]], 50]

%Y Cf. A007304, A046528, A144856.

%K nonn

%O 1,1

%A _Timothy L. Tiffin_, Jul 06 2021