

A101848


Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n1) + 81 for n > 0.


1



0, 16, 18, 28, 42, 118, 172, 948, 1608, 5578, 19678, 34146, 43492, 97798
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OFFSET

1,2


COMMENTS

Numbers n such that (360*10^n  81)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 9 followed by digit 1 is prime.
Numbers corresponding to terms <= 948 are certified primes.
a(15) > 10^5.  Robert Price, Mar 17 2015


REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462467.


LINKS

Table of n, a(n) for n=1..14.
Makoto Kamada, Prime numbers of the form 399...991.
Index entries for primes involving repunits.


FORMULA

a(n) = A101396(n)  1.


EXAMPLE

31 is prime, hence 0 is a term.


MATHEMATICA

Select[Range[0, 1000], PrimeQ[(360*10^#  81)/9] &] (* Robert Price, Mar 17 2015 *)


PROG

(PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+81)
(PARI) for(n=0, 1500, if(isprime((360*10^n81)/9), print1(n, ", ")))


CROSSREFS

Cf. A000533, A002275, A101396.
Sequence in context: A057369 A178110 A117100 * A032401 A223588 A183401
Adjacent sequences: A101845 A101846 A101847 * A101849 A101850 A101851


KEYWORD

nonn,hard,more


AUTHOR

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


EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(12)a(14) derived from A101396 by Robert Price, Mar 17 2015


STATUS

approved



