A101964 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 33 for n > 0.

0, 1, 2, 4, 5, 6, 10, 20, 29, 67, 72, 168, 175, 344, 822, 1020, 1190, 2072, 2754, 10716, 14672, 16753, 17605, 81028, 120850, 167964, 200407

Offset: 1

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004

Keywords

• nonn
• hard
• more

Comments

Numbers n such that (240*10^n - 33)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 6 followed by digit 3 is prime.

Numbers corresponding to terms <= 822 are certified primes.

a(28) > 3*10^5. - Robert Price, Jul 13 2023

Examples

			263 is prime, hence 1 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 266...663.
• Index entries for primes involving repunits.

Crossrefs

Cf. A000533, A002275, A098959.

Programs

PARI

a=23;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+33)

PARI

for(n=0,1500,if(isprime((240*10^n-33)/9),print1(n,",")))

Formula

a(n) = A098959(n) - 1.

Extensions

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

a(24) derived from A098959 by Robert Price, Jan 17 2015

a(25)-a(27) derived from A098959 by Robert Price, Jul 13 2023