A240170 Larger of the greatest cousin prime pair with n digits.

7, 83, 971, 9887, 99881, 999983, 9999401, 99999551, 999999761, 9999999707, 99999999947, 999999998867, 9999999999083, 99999999999467, 999999999997841, 9999999999997031, 99999999999998717, 999999999999999161, 9999999999999996587, 99999999999999999803

Offset: 1

Author

Abhiram R Devesh, Aug 02 2014

Keywords

• nonn
• base

Comments

The sum of the reciprocals converges to 0.156047....

It is only a (plausible) conjecture that this sequence is well-defined. See A152052. - N. J. A. Sloane, Aug 22 2014

Links

• Abhiram R Devesh, Table of n, a(n) for n = 1..100
• Eric Weisstein's World of Mathematics, Cousin Primes

Crossrefs

Cf. A046132, A152052, A240167.

Analogous sequences with twin primes:

- A092245 Lesser of the first twin prime pair with n digits.

- A114429 Larger of the greatest twin prime pair with n digits.

Programs

PARI

a(n)=p=precprime(10^n);while(!isprime(p-4),p=precprime(p-1));return(p)
vector(50, n, a(n)) \\ Derek Orr, Aug 04 2014

Python

import sympy
for i in range(1,100):
    a=(10**i)
    p=sympy.prevprime(a)
    while sympy.isprime(p-4)==False:
        p=sympy.prevprime(p)
    print(p)