login
A082549
Numbers n such that concatenation of first n primes, separated by zeros, is prime.
3
1, 9, 15, 25, 59, 444
OFFSET
1,2
COMMENTS
w_n= (p_1)0(p_2)0(p_3)...0(p_n) w_1=2 is prime(a_1=1), w_2, ..., w_8 are not prime and w_9 is prime (a_2=9),... a_n is the n-th term of w_n which is prime.
a(7) > 2615. - Derek Orr, Aug 12 2014
EXAMPLE
a(2)=9 because 2030507011013017019023, which is the concatenation of first 9 primes separated by zeros is prime.
MATHEMATICA
Select[Range[450], PrimeQ[FromDigits[Flatten[IntegerDigits/@Riffle[ Prime[ Range[ #]], 0]]]]&] (* Harvey P. Dale, Feb 28 2020 *)
PROG
(PARI)
p=""; for(n=1, 5000, p=concat(p, "0"); p=concat(p, Str(prime(n))); if(ispseudoprime(eval(p)), print1(n, ", "))) \\ Derek Orr, Aug 12 2014
CROSSREFS
Sequence in context: A193227 A014003 A333788 * A013569 A129401 A164385
KEYWORD
base,hard,more,nonn
AUTHOR
Farideh Firoozbakht, May 03 2003
STATUS
approved