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A101841 Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 61 for n > 0. 1
0, 4, 70, 111, 114, 172, 262, 309, 357, 10498, 22924, 37956, 254194 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (340*10^n - 61)/9 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime.

Numbers corresponding to terms <= 357 are certified primes.

a(14) >= 4*10^5. - Jason H Parker, Jun 15 2019

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..13.

Makoto Kamada, Prime numbers of the form 377...771.

Index entries for primes involving repunits.

FORMULA

a(n) = A102976(n) - 1. [adapted by Georg Fischer, Jan 04 2021]

EXAMPLE

377771 is prime, hence 4 is a term.

MATHEMATICA

Select[Range[0, 300], PrimeQ[(340*10^# - 61)/9] &] (* Robert Price, May 08 2015 *)

PROG

(PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61)

(PARI) for(n=0, 1500, if(isprime((340*10^n-61)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A102976.

Sequence in context: A065573 A308294 A278553 * A274873 A281654 A222309

Adjacent sequences:  A101838 A101839 A101840 * A101842 A101843 A101844

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004

EXTENSIONS

a(10)-a(12) from Kamada data by Ray Chandler, May 01 2015

a(13) from Jason H Parker, Jun 15 2019

STATUS

approved

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Last modified December 6 06:14 EST 2021. Contains 349563 sequences. (Running on oeis4.)