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A102011 Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 61 for n > 0. 2
0, 2, 5, 50, 56, 62, 149, 392, 419, 546, 42023, 43062 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (110*10^n + 61)/9 is prime.

Numbers n such that digit 1 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.

Numbers corresponding to terms <= 546 are certified primes.

a(13) > 10^5. - Robert Price, Jan 17 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..12.

Makoto Kamada, Prime numbers of the form 122...229.

Index entries for primes involving repunits.

FORMULA

a(n) = A102931(n) - 1.

EXAMPLE

1222229 is prime, hence 5 is a term.

PROG

(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61)

(PARI) for(n=0, 1500, if(isprime((110*10^n+61)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A102931.

Sequence in context: A060808 A099658 A244014 * A208797 A004098 A208206

Adjacent sequences:  A102008 A102009 A102010 * A102012 A102013 A102014

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004

EXTENSIONS

a(11)-a(12) derived from A102931 by Robert Price, Jan 17 2015

STATUS

approved

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Last modified February 21 22:56 EST 2018. Contains 299427 sequences. (Running on oeis4.)