login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A101970 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 53 for n > 0. 1
0, 1, 6, 27, 72, 294, 493, 597, 2599, 3729, 7548, 15864 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Numbers n such that (260*10^n - 53)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 8 followed by digit 3 is prime.

Numbers corresponding to terms <= 597 are certified primes.

a(13) > 10^5. - Robert Price, Apr 18 2014

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..12.

Makoto Kamada, Prime numbers of the form 288...883.

Index entries for primes involving repunits.

FORMULA

a(n) = A102961(n+1) - 1.

EXAMPLE

283 is prime, hence 1 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(260*10^# - 53)/9] &] (* Robert Price, Apr 18 2015 *)

PROG

(PARI) a=23; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+53)

(PARI) for(n=0, 1500, if(isprime((260*10^n-53)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A102961.

Sequence in context: A273408 A085788 A027276 * A136105 A239568 A198958

Adjacent sequences:  A101967 A101968 A101969 * A101971 A101972 A101973

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(12) derived from A102961 by Robert Price, Apr 18 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 21 18:44 EST 2020. Contains 332107 sequences. (Running on oeis4.)