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
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
(Python)
from itertools import chain, accumulate, count, islice
from operator import mul
from sympy import prime
def A225727_gen(): return (i+1 for i, m in enumerate(accumulate(accumulate(chain((1, ), (prime(n) for n in count(1))), mul))) if m % (i+1) == 0)
A225727_list = list(islice(A225727_gen(), 6)) # Chai Wah Wu, Feb 23 2022
CROSSREFS
Sequence in context: A011917 A018691 A332869 * A163943 A093418 A173733
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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 27 16:21 EST 2024. Contains 370378 sequences. (Running on oeis4.)