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A103163 a(n) = gcd(reverse(prime(n)), reverse(prime(n+1))). 1
1, 1, 1, 1, 1, 1, 1, 1, 4, 1, 1, 1, 2, 2, 1, 5, 1, 4, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 14, 2, 2, 2, 4, 2, 2, 8, 2, 2, 2, 4, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 13, 8, 2, 2, 2, 2, 2, 2, 8, 2, 2, 4, 4, 2, 2, 2, 2, 1, 5, 5, 25, 5, 5, 5, 5, 5, 5, 25, 5, 5, 5, 1, 2, 2, 4, 4, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,9
COMMENTS
Greatest common divisor of two consecutive primes after each prime is written backward.
LINKS
FORMULA
a(n) = gcd(A004087(n), A004087(n+1)).
EXAMPLE
Neither of these common divisors are divisible by 3 or by 10 or by 11.
MAPLE
A103163 := proc(n)
p := ithprime(n) ;
q := nextprime(p) ;
igcd(digrev(p), digrev(q)) ;
end proc:
seq(A103163(n), n=1..114) ; # R. J. Mathar, Sep 22 2018
MATHEMATICA
rd[x_] :=FromDigits[Reversed[IntegerDigits[x]]]; Table[GCD[rd[Prime[w]], rd[Prime[w+1]]], {w, 1, 1000}]
GCD@@#&/@(Partition[IntegerReverse/@Prime[Range[120]], 2, 1]) (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 31 2020 *)
CROSSREFS
Sequence in context: A336722 A073802 A132157 * A128211 A348986 A199393
KEYWORD
base,nonn
AUTHOR
Labos Elemer, Jan 27 2005
EXTENSIONS
Edited by Jon E. Schoenfield, Oct 26 2019
STATUS
approved

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Last modified April 20 15:59 EDT 2024. Contains 371844 sequences. (Running on oeis4.)