1,2

Indices of primes in sequence defined by A(0) = 99, A(n) = 10*A(n-1) + 21 for n > 0. - Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

Numbers n such that (830*10^n + 61)/9 is prime. - Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

a(n) = A082718(n-1) - 2.

Numbers corresponding to terms <= 109 are certified primes. For number corresponding to 3607 see P. De Geest, PDP Reference Table.

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

P. De Geest, PDP Reference Table

Makoto Kamada, Factorizations of 922...229.

9222229 is prime, hence 5 is a term.

Do[If[PrimeQ[(9*10^n + 2*(10^n - 1)/9)*10 + 9], Print[n]], {n, 1, 2500}]

(PARI) a=99; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-61) - Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

(PARI) for(n=0, 1000, if(isprime((830*10^n + 61)/9), print1(n, ", "))) - Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

Cf. A000533, A002275, A082718.

Sequence in context: A062652 A075706 A057178 this_sequence A041909 A041048 A094108

Adjacent sequences: A056262 A056263 A056264 this_sequence A056266 A056267 A056268

hard,nonn,base,more

Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 18 2000

3607 from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

37785 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

Edited by N. J. A. Sloane (njas(AT)research.att.com), Jan 14 2008