A108251 Numbers n such that googol - n is prime.

797, 911, 1287, 2127, 2217, 2247, 2303, 2457, 2841, 3221, 3407, 3531, 3921, 4353, 4361, 4403, 5097, 5459, 5867, 6173, 6261, 6531, 6741, 6939, 7133, 7271, 7311, 7707, 7797, 8651, 8841, 8951, 9347, 9401, 9599, 9669, 9729, 10001, 10773, 10937, 11663

Offset: 1

Author

Cino Hilliard, Jun 17 2005

Keywords

• easy
• nonn
• fini

Comments

This sequence is finite with between 4.361969*10^97 and 4.361998*10^97 terms. Under the Riemann Hypothesis, it has 4.361971987140703159099509113229164611538757211...*10^97 terms. - Charles R Greathouse IV, Nov 23 2009

10^100-a(148) and 10^100-a(149) are the last twin primes less than 10^100. - T. D. Noe, Nov 03 2008

Examples

			A googol = 10^100. 10^100 - 797 is prime, so 797 is in the sequence.
		

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000
• For each of the 1000 terms in the table, 10^100 - a(n) was verified by the Magma Calculator as prime. - _Jon E. Schoenfield_, Aug 24 2009

Crossrefs

Cf. A049014, A133282.

Programs

Mathematica

Rest[10^100-#&/@NestList[NextPrime[#,-1]&,10^100,50]] (* Harvey P. Dale, Jan 23 2017 *)

PARI

forstep(x=1,n,2,if(isprime(10^100-x),print1(x",")))

Extensions

Edited by Charles R Greathouse IV, Nov 23 2009