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A088982
Primes that are between consecutive prime-indexed primes.
4
7, 13, 19, 23, 29, 37, 43, 47, 53, 61, 71, 73, 79, 89, 97, 101, 103, 107, 113, 131, 137, 139, 149, 151, 163, 167, 173, 181, 193, 197, 199, 223, 227, 229, 233, 239, 251, 257, 263, 269, 271, 281, 293, 307, 311, 313, 317, 337, 347, 349, 359, 373, 379, 383, 389
OFFSET
1,1
COMMENTS
Conjecture: For x > 1 there is at least 1 prime between prime(prime(x)) and prime(prime(x+1)).
This conjecture is equivalent to saying that there is at least one prime index between prime(x) and prime(x+1), which is trivially true because both are odd for x > 1; one has prime(prime(x)) < prime(prime(x)+1) < prime(prime(x+1)). Obviously the definition is equivalent to "primes > 2 with nonprime index", i.e., sequence A007821 without the initial 2. - M. F. Hasler, Jul 31 2015
LINKS
FORMULA
Primes p such that prime(prime(x)) < p < prime(prime(x+1)).
a(n) = prime(composite(n)) = A000040(A002808(n)). - Terry D. Grant, Aug 16 2016
EXAMPLE
Prime(prime(4)) = 17 and prime(prime(5)) = 31 and 19,23,29 are between 17 and 31, so 19, 23 and 29 are members.
MATHEMATICA
Flatten[Table[Prime[Range[Prime[n]+1, Prime[n+1]-1]], {n, 30}]] (* Harvey P. Dale, Mar 22 2015 *)
PROG
(PARI) pipprimes(n) = { for(x=1, n, c=-2; p1 = prime(prime(x)); p2 = prime(prime(x+1)); forprime(y=p1, p2, c++; if(y > p1 && y < p2, print1(y", ")); ); ) }
(PARI) forcomposite(n=2, 100, print1(prime(n)", ")) \\ M. F. Hasler, Jul 31 2015
CROSSREFS
Essentially the same as A007821.
Sequence in context: A371166 A340105 A309649 * A354460 A176406 A033561
KEYWORD
nonn
AUTHOR
Cino Hilliard, Oct 31 2003
STATUS
approved