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A168159 Distance of the least reversible n-digit prime from 10^(n-1) 1
1, 1, 1, 9, 7, 49, 33, 169, 7, 7, 207, 237, 91, 313, 261, 273, 79, 49, 2901, 51, 441, 193, 9, 531, 289, 1141, 67, 909, 331, 753, 2613, 657, 49, 4459, 603, 1531, 849, 2049, 259, 649, 2119, 1483, 63, 6747, 519, 3133, 937, 1159, 1999, 6921, 2949, 613, 4137, 1977, 31 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

A (much) more compact form of A114018 (cf. formula). Since this sequence and A114018 refer to "reversible primes" (A007500), while A122490 seems to use "emirps" (A006567), a(n+1) differs from A122490(n) iff 10^n+1 is prime <=> a(n+1)=1 <=> A114018(n)=10^n+1.

LINKS

Table of n, a(n) for n=1..55.

FORMULA

a(n)=A114018(n)-10^(n-1)

MATHEMATICA

Table[p = NextPrime[y = 10^(n - 1)]; While[! PrimeQ[FromDigits[Reverse[IntegerDigits[p]]]], p = NextPrime[p]]; p - y, {n, 55}] (* Jayanta Basu, Aug 09 2013 *)

PROG

(PARI) for(x=1, 1e99, until( isprime(x=nextprime(x+1)) & isprime(eval(concat(vecextract(Vec(Str(x)), "-1..1")))), ); print1(x-10^ (#Str(x)-1), ", "); x=10^#Str(x)-1)

CROSSREFS

Sequence in context: A298780 A231605 A248307 * A038297 A144622 A069242

Adjacent sequences:  A168156 A168157 A168158 * A168160 A168161 A168162

KEYWORD

base,nonn

AUTHOR

M. F. Hasler, Nov 21 2009

STATUS

approved

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Last modified June 25 09:48 EDT 2019. Contains 324347 sequences. (Running on oeis4.)