

A101061


Indices of primes in sequence defined by A(0) = 81, A(n) = 10*A(n1) + 11 for n > 0.


1




OFFSET

1,2


COMMENTS

Numbers n such that (740*10^n  11)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.
Numbers corresponding to terms <= 176 are certified primes.
a(9) > 10^5.  Robert Price, Oct 13 2015


REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462467.


LINKS

Table of n, a(n) for n=1..8.
Makoto Kamada, Prime numbers of the form 822...221.
Index entries for primes involving repunits.


FORMULA

a(n) = A103074(n+1)  1.  Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008


EXAMPLE

822221 is prime, hence 4 is a term.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(740*10^#  11)/9] &] (* Robert Price, Oct 13 2015 *)


PROG

(PARI) a=81; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+11)
(PARI) for(n=0, 1000, if(isprime((740*10^n11)/9), print1(n, ", ")))


CROSSREFS

Cf. A000533, A002275, A103074.
Sequence in context: A133465 A110128 A148279 * A148280 A112638 A077162
Adjacent sequences: A101058 A101059 A101060 * A101062 A101063 A101064


KEYWORD

nonn,hard,more


AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwthaachen.de), Nov 30 2004


EXTENSIONS

8461 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(8) from Erik Branger May 01 2013 by Ray Chandler, Apr 29 2015


STATUS

approved



