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A101068 Indices of primes in sequence defined by A(0) = 87, A(n) = 10*A(n-1) - 23 for n > 0. 1
2, 4, 100, 104, 4096, 5732, 9754, 31832 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (760*10^n + 23)/9 is prime.

Numbers n such that digit 8 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime.

Numbers corresponding to terms <= 104 are certified primes.

a(9) > 10^5. - Robert Price, Oct 18 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..8.

Makoto Kamada, Prime numbers of the form 844...447.

Index entries for primes involving repunits.

FORMULA

a(n) = A103081(n+1) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

EXAMPLE

8447 is prime, hence 2 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(760*10^# + 23)/9] &] (* Robert Price, Oct 18 2015 *)

PROG

(PARI) a=87; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-23)

(PARI) for(n=0, 1000, if(isprime((760*10^n + 23)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103081.

Sequence in context: A092918 A018428 A128773 * A018435 A166094 A018440

Adjacent sequences:  A101065 A101066 A101067 * A101069 A101070 A101071

KEYWORD

nonn,hard,more

AUTHOR

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

EXTENSIONS

More terms 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

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Last modified September 17 11:15 EDT 2019. Contains 327129 sequences. (Running on oeis4.)