A082549 Numbers n such that concatenation of first n primes, separated by zeros, is prime.

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

Links

Table of n, a(n) for n=1..6.

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

Adjacent sequences: A082546 A082547 A082548 * A082550 A082551 A082552

Keyword

base,hard,more,nonn

Author

Farideh Firoozbakht, May 03 2003

Status

approved