A101828 Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 11 for n > 0.

0, 2, 5, 11, 407, 648, 948, 962, 1004, 2699, 19778, 22517, 22610, 40583, 55361, 70193

Offset

1,2

Comments

Numbers n such that (290*10^n - 11)/9 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.

Numbers corresponding to terms <= 962 are certified primes.

a(17) > 10^5. - Robert Price, Apr 04 2015

References

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

Links

Table of n, a(n) for n=1..16.

Makoto Kamada, Prime numbers of the form 322...221.

Index entries for primes involving repunits.

Formula

a(n) = A102966(n+1) - 1.

Example

3221 is prime, hence 2 is a term.

Mathematica

Select[Range[0, 1000], PrimeQ[(290*10^# - 11)/9] &](* Robert Price, Apr 04 2015 *)

Prog

(PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+11)
(PARI) for(n=0, 1500, if(isprime((290*10^n-11)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102966.

Sequence in context: A107989 A069504 A158997 * A071293 A234572 A341804

Adjacent sequences: A101825 A101826 A101827 * A101829 A101830 A101831

Keyword

nonn,hard,more

Author

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

Extensions

2699 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(11)-a(16) derived from A102966 by Robert Price, Apr 04 2015

Status

approved