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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.

Sequence in context: A075452 A020258 A098368 this_sequence A061442 A049514 A049518

Adjacent sequences: A101063 A101064 A101065 this_sequence A101067 A101068 A101069

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 probable primes, from Ryan Propper (rpropper(AT)stanford.edu), Jun 20 2005

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

Edited by T. D. Noe (noe(AT)sspectra.com), Oct 30 2008

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.


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