1,1

4-almost prime analogue of primorial primes A005234 (primes p such that 1 + product of primes up to p is prime) as indexed by A014545 (n such that n-th Euclid number (A006862(n)) = 1 + (Product of first n primes) is prime). In that sense, this sequence is indexed by (1, 8, ...). No more through product of first 16 of the 4-almost primes.

{a(n)} = {1 + Prod[from i = 1 to n] A014613(i)} INTERSECTION {A000040}.

a(1) = 17 because 1 + 16 = 1 + A014613(1) = 1 more than the first 4-almost prime is itself prime.

a(2) = 8126654054401 = 1 + (16 * 24 * 36 * 40 * 54 * 56 * 60 * 81) = 1 more than the product of the first 8 of the 4-almost primes, and is prime.

Cf. A000040, A001358, A014612, A002110, A005234, A014545, A112141.

Sequence in context: A013806 A104536 A013882 this_sequence A134686 A128398 A072839

Adjacent sequences: A114429 A114430 A114431 this_sequence A114433 A114434 A114435

bref,easy,nonn

Jonathan Vos Post (jvospost3(AT)gmail.com), Feb 13 2006