A102010 Indices of primes in sequence defined by A(0) = 17, A(n) = 10*A(n-1) - 43 for n > 0.

0, 1, 3, 13, 24, 31, 55, 61, 810, 811, 1083, 2532, 11923, 49551

Offset: 1

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004

Keywords

• nonn
• hard
• more

Comments

Numbers n such that (110*10^n + 43)/9 is prime.

Numbers n such that digit 1 followed by n >= 0 occurrences of digit 2 followed by digit 7 is prime.

Numbers corresponding to terms <= 811 are certified primes.

a(15) > 10^5. - Robert Price, Jan 16 2015

a(15) > 2*10^5. - Tyler Busby, Feb 01 2023

Examples

			12227 is prime, hence 3 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 122...227.
• Index entries for primes involving repunits.

Crossrefs

Cf. A000533, A002275, A102930.

Programs

PARI

a=17;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-43)

PARI

for(n=0,1500,if(isprime((110*10^n+43)/9),print1(n,",")))

Formula

a(n) = A102930(n) - 1.

Extensions

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

a(13)-a(14) derived from A102930 by Robert Price, Jan 16 2015