A101967 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 43 for n > 0.

0, 3, 9, 164, 227, 383, 2889, 3444, 10068, 17355, 25803, 29051, 29081

Offset

1,2

Comments

Numbers n such that (250*10^n - 43)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 7 followed by digit 3 is prime.

Numbers corresponding to terms <= 383 are certified primes.

a(14) > 10^5. - Robert Price, Mar 01 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 277...773.

Index entries for primes involving repunits.

Formula

a(n) = A102958(n+1) - 1.

Example

27773 is prime, hence 3 is a term.

Prog

(PARI) a=23; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+43)
(PARI) for(n=0, 1500, if(isprime((250*10^n-43)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A102958.

Sequence in context: A087193 A348141 A217638 * A078590 A358704 A061963

Adjacent sequences: A101964 A101965 A101966 * A101968 A101969 A101970

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004

Extensions

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

a(9)-a(13) derived from A102958 by Robert Price, Mar 01 2015

Status

approved