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A101578 Indices of primes in sequence defined by A(0) = 51, A(n) = 10*A(n-1) + 31 for n > 0. 1
1, 2, 85, 133, 184, 343, 395, 475, 833, 1798, 2146, 2417, 5215, 5881, 6215, 13393, 19745, 66484 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (490*10^n - 31)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 4 followed by digit 1 is prime.

a(19) > 10^5. - Robert Price, Jul 16 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..18.

Makoto Kamada, Prime numbers of the form 544...441.

Index entries for primes involving repunits.

FORMULA

a(n) = A103013(n+1) - 1.

EXAMPLE

5441 is prime, hence 2 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(490*10^#-31)/9]&] (* Robert Price, Jul 16 2015 *)

PROG

(PARI) a=51; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+31)

(PARI) for(n=0, 1000, if(isprime((490*10^n-31)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103013.

Sequence in context: A157315 A244947 A078166 * A041881 A076542 A226842

Adjacent sequences:  A101575 A101576 A101577 * A101579 A101580 A101581

KEYWORD

nonn,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004

EXTENSIONS

3 more terms from Ryan Propper, Jun 16 2005

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007

a(16)-a(17) by Ray Chandler, Apr 24 2015

a(18) from Robert Price, Jul 16 2015

STATUS

approved

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Last modified April 21 21:03 EDT 2018. Contains 302877 sequences. (Running on oeis4.)