A101839 Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 51 for n > 0.

0, 5, 10, 12, 18, 22, 66, 107, 117, 175, 672, 779, 1087, 1218, 1655, 6244, 10738, 12589, 17512, 25999, 32543, 53273

Offset

1,2

Comments

Numbers n such that (330*10^n - 51)/9 is prime.

Numbers n such that digit 3 followed by n >= 0 occurrences of digit 6 followed by digit 1 is prime.

a(23) > 10^5. - Robert Price, Jan 29 2015

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..22.

Makoto Kamada, Prime numbers of the form 366...661.

Index entries for primes involving repunits.

Formula

a(n) = A102974(n) - 1. [adapted by Georg Fischer, Jan 04 2021]

Example

3666661 is prime, hence 5 is a term.

Prog

(PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+51)
(PARI) for(n=0, 1500, if(isprime((330*10^n-51)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102974.

Sequence in context: A313367 A313368 A313369 * A228312 A313370 A313371

Adjacent sequences: A101836 A101837 A101838 * A101840 A101841 A101842

Keyword

nonn,hard,more

Author

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

Extensions

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

a(17)-a(22) derived from A102974 by Robert Price, Jan 29 2015

Status

approved