This site is supported by donations to The OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A285528 Numbers n such that A217723(n) (sum of first n primorial numbers minus 1) is prime. 0
 2, 3, 5, 6, 7, 8, 11, 14, 21, 41, 42, 43, 74, 78 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This sequence is finite since 463 (the 90th prime) divides A217723(89) and thus all the succeeding terms of A217723 are also divisible by 463. The associated primes are: 7, 37, 2557, 32587, 543097, 10242787, 207263519017, 13394639596851067, 41295598995285955839203627497, 2.998... * 10^70, 5.427... * 10^72, 1.036... * 10^75, 4.549... * 10^150 and 1.019... * 10^161. They are a subsequence of A127729. LINKS EXAMPLE A217723(5) = 2 + 2*3 + 2*3*5 + 2*3*5*7 + 2*3*5*7*11 - 1 = 2557 is prime, thus 5 is in this sequence. MAPLE select(m -> isprime(add(mul(ithprime(i), i=1..j), j=1..m)-1), [\$1..89]); # Robert Israel, Apr 20 2017 MATHEMATICA primorial[n_] := Product[Prime[i], {i, n}]; a[n_] := Sum[primorial[i], {i, 1, n}]-1; Select[Range[0, 100], PrimeQ[a[#]] &] (* Second program: *) Flatten@ Position[Accumulate@ FoldList[#1 #2 &, Prime@ Range@ 200] - 1 /. k_ /; k == 1 || CompositeQ@ k -> 0, m_ /; m != 0] (* Michael De Vlieger, Apr 23 2017 *) CROSSREFS Cf. A002110, A217723, A127729, A223546. Sequence in context: A016741 A191167 A006431 * A151894 A028229 A104452 Adjacent sequences:  A285525 A285526 A285527 * A285529 A285530 A285531 KEYWORD nonn,fini,full AUTHOR Amiram Eldar, Apr 20 2017 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 14 04:56 EST 2019. Contains 329110 sequences. (Running on oeis4.)