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A101740 Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) + 27 for n > 0. 1
0, 14, 40, 63, 130, 137, 191, 286, 494, 965, 1090, 1365, 1713, 1773, 3252, 6330, 35325, 36990, 59585, 88260, 127178 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (450*10^n - 27)/9 is prime.

Numbers n such that digit 4 followed by n >= 0 occurrences of digit 9 followed by digit 7 is prime.

Numbers corresponding to terms <= 965 are certified primes.

a(22) > 2*10^5. - Robert Price, Jul 09 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..21.

Makoto Kamada, Prime numbers of the form 499...997.

Index entries for primes involving repunits.

FORMULA

a(n) = A103003(n+1) - 1.

EXAMPLE

4999999999999997 is prime, hence 14 is a term.

PROG

(PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+27)

(PARI) for(n=0, 1500, if(isprime((450*10^n-27)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103003.

Sequence in context: A162266 A181149 A019063 * A069126 A124707 A126368

Adjacent sequences:  A101737 A101738 A101739 * A101741 A101742 A101743

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(17)-a(20) from Kamada data by Ray Chandler, May 01 2015

a(21) from Robert Price, Jul 09 2015

STATUS

approved

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Last modified June 1 17:40 EDT 2020. Contains 334762 sequences. (Running on oeis4.)