login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A225727 Numbers n such that sum of first n primorials (A143293) is divisible by n. 2
1, 3, 17, 51, 967, 2901, 16439, 49317, 147951, 1331559 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(5) = 967 is a prime,

a(6) = a(5) * 3,

a(7) = a(5) * 17,

a(8) = a(5) * 51,

a(9) = a(5) * 51 * 3,

a(10) = a(5) * 51 * 27.

The next term, if it exists, is greater than 15600000. - Alex Ratushnyak, Jun 16 2013

LINKS

Table of n, a(n) for n=1..10.

EXAMPLE

Sum of first 3 primorials is 1+2+6=9, because 9 is divisible by 3, the latter is in the sequence.

Sum of first 17 primorials is A143293(17) = 1955977793053588026279. Because A143293(17) is divisible by 17, the latter is in the sequence.

PROG

(Python)

primes = [2]*2

primes[1] = 3

def addPrime(k):

  for p in primes:

    if k%p==0:  return

    if p*p > k:  break

  primes.append(k)

for n in range(5, 10000000, 6):

  addPrime(n)

  addPrime(n+2)

sum = 0

primorial = n = 1

for p in primes:

  sum += primorial

  primorial *= p

  if sum % n == 0:  print n,

  n += 1

CROSSREFS

Cf. A143293, A002110, A057245, A128981.

Sequence in context: A011917 A018691 A332869 * A163943 A093418 A173733

Adjacent sequences:  A225724 A225725 A225726 * A225728 A225729 A225730

KEYWORD

nonn,hard,more

AUTHOR

Alex Ratushnyak, May 13 2013

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 23 03:15 EST 2022. Contains 350504 sequences. (Running on oeis4.)