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

Table of n, a(n) for n=1..21.

Makoto Kamada, Prime numbers of the form 300...001.

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

Cf. A000533, A002275, A056807.

Sequence in context: A244427 A121624 A103019 * A242421 A093397 A332066

Adjacent sequences: A101820 A101821 A101822 * A101824 A101825 A101826

Keyword

nonn,more

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