A101527 Indices of primes in sequence defined by A(0) = 61, A(n) = 10*A(n-1) + 31 for n > 0.

0, 1, 6, 18, 24, 36, 48, 132, 612, 1339, 2035, 2490, 26262

Offset

1,3

Comments

Numbers n such that (580*10^n - 31)/9 is prime.

Numbers n such that digit 6 followed by n >= 0 occurrences of digit 4 followed by digit 1 is prime.

Numbers corresponding to terms <= 612 are certified primes.

a(14) > 10^5. - Robert Price, Sep 10 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..13.

Makoto Kamada, Prime numbers of the form 644...441.

Index entries for primes involving repunits.

Formula

a(n) = A103034(n+1) - 1.

Example

641 is prime, hence 1 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(580*10^# - 31)/9] &] (* Robert Price, Sep 10 2015 *)

Prog

(PARI) a=61; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+31)
(PARI) for(n=0, 1500, if(isprime((580*10^n-31)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103034.

Sequence in context: A011775 A015707 A236864 * A028887 A283118 A274536

Adjacent sequences: A101524 A101525 A101526 * A101528 A101529 A101530

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004

Extensions

Two more terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 22 2007

a(13) from Max Alekseyev, Dec 12 2011

Status

approved