

A101848


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


0



0, 16, 18, 28, 42, 118, 172, 948, 1608, 5578, 19678
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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.


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..11.
Makoto Kamada, Factorizations of nearrepdigit numbers.


EXAMPLE

31 is prime, hence 0 is a term.


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.
a(n) = A101396(n)  1.
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


STATUS

approved



