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A101066 Indices of primes in sequence defined by A(0) = 81, A(n) = 10*A(n-1) + 31 for n > 0. +0
1
25, 35, 37, 59, 79, 91, 173, 485, 626, 998, 1613, 4381, 4897, 8441 (list; graph; listen)
OFFSET

1,1

COMMENT

Numbers n such that (760*10^n - 31)/9 is prime.

Numbers n such that digit 8 followed by n >= 0 occurrences of digit 4 followed by digit 1 is prime.

Numbers corresponding to terms <= 626 are certified primes.

Next term after 4897 is greater than 10000. - Ryan Propper (rpropper(AT)stanford.edu), Jun 20 2005

REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

LINKS

Makoto Kamada, Factorizations of near-repdigit numbers.

FORMULA

a(n) = A103079(n) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

EXAMPLE

844444444444444444444444441 is prime, hence 25 is a term.

PROGRAM

(PARI) a=81; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+31)

(PARI) for(n=0, 1000, if(isprime((760*10^n-31)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275.

Adjacent sequences: A101063 A101064 A101065 this_sequence A101067 A101068 A101069

Sequence in context: A075452 A020258 A098368 this_sequence A061442 A049514 A049518

KEYWORD

nonn,hard,more

AUTHOR

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

EXTENSIONS

Three additional terms, corresponding to pseudoprimes, from Ryan Propper (rpropper(AT)stanford.edu), Jun 20 2005

One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

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Last modified October 13 02:37 EDT 2008. Contains 145008 sequences.


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