

A101954


Indices of primes in sequence defined by A(0) = 27, A(n) = 10*A(n1)  53 for n > 0.


1




OFFSET

1,1


COMMENTS

Numbers n such that (190*10^n + 53)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime.
Numbers corresponding to terms <= 392 are certified primes.
No further terms up to n=5000. [Harvey P. Dale, Aug 20 2011]
a(7) > 10^5.  Robert Price, Feb 07 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..6.
Makoto Kamada, Factorizations of 211...117.
Index entries for primes involving repunits.


FORMULA

a(n) = A102949(n)  1.


EXAMPLE

2111111111111111111111111111111111117 is prime, hence 35 is a term.


MATHEMATICA

a = 27; Flatten[Position[Table[a = 10*a  53, {n, 500}], _?(PrimeQ[#] &)]]


PROG

(PARI) a=27; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a53)
(PARI) for(n=0, 1500, if(isprime((190*10^n+53)/9), print1(n, ", ")))


CROSSREFS

Cf. A000533, A002275, A102949.
Sequence in context: A219825 A194716 A220047 * A220201 A005937 A219831
Adjacent sequences: A101951 A101952 A101953 * A101955 A101956 A101957


KEYWORD

nonn,hard,more,changed


AUTHOR

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


EXTENSIONS

a(5)a(6) derived from A102949 by Robert Price, Feb 07 2015


STATUS

approved



