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A101823

Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) - 9 for n > 0.

0, 2, 6, 9, 27, 35, 66, 80, 146, 482, 642, 1019, 1899, 2619, 10452, 27719, 52823, 105588, 111987, 618852, 665828

OFFSET

1,2

COMMENTS

Numbers n such that 30*10^n + 1 is prime.

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

REFERENCES

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

LINKS

FORMULA

a(n) = A056807(n) - 1.

EXAMPLE

3001 is prime, hence 2 is a term.

PROG

(PARI) a=31; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a-9)

(PARI) for(n=0, 2000, if(isprime(30*10^n+1), print1(n, ", ")))

CROSSREFS

KEYWORD

nonn,more,hard

AUTHOR

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

EXTENSIONS

More terms from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(18) from Roman Makarchuk, Dec 05 2008 confirmed as next term by Ray Chandler, Mar 02 2012

a(19) from Alexander Gramolin, Feb 24 2012 confirmed as next term by Ray Chandler, Mar 02 2012

a(20)-a(21) derived from A056807 by Robert Price, Jan 26 2015

STATUS

approved

URL: https://oeis.org/A101823