A101823 Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) - 9 for n > 0.

0, 2, 6, 9, 27, 35, 66, 80, 146, 482, 642, 1019, 1899, 2619, 10452, 27719, 52823, 105588, 111987, 618852, 665828

Offset: 1

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004

Keywords

• nonn
• more
• hard

Comments

Numbers n such that 30*10^n + 1 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 0 followed by digit 1 is prime.

Examples

			3001 is prime, hence 2 is a term.
		

References

• Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Links

• Makoto Kamada, Prime numbers of the form 300...001.

Crossrefs

Cf. A000533, A002275, A056807.

Programs

PARI

a=31;for(n=0,2000,if(isprime(a),print1(n,","));a=10*a-9)

PARI

for(n=0,2000,if(isprime(30*10^n+1),print1(n,",")))

Formula

a(n) = A056807(n) - 1.

Extensions

More terms from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(18) from Roman Makarchuk, Dec 05 2008 confirmed as next term by Ray Chandler, Mar 02 2012

a(19) from Alexander Gramolin, Feb 24 2012 confirmed as next term by Ray Chandler, Mar 02 2012

a(20)-a(21) derived from A056807 by Robert Price, Jan 26 2015