A103163 a(n) = gcd(reverse(prime(n)), reverse(prime(n+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

Offset

1,9

Comments

Greatest common divisor of two consecutive primes after each prime is written backward.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

Cf. A004087, A000040.

Sequence in context: A336722 A073802 A132157 * A128211 A348986 A199393

Adjacent sequences: A103160 A103161 A103162 * A103164 A103165 A103166

Keyword

base,nonn

Author

Labos Elemer, Jan 27 2005

Extensions

Edited by Jon E. Schoenfield, Oct 26 2019

Status

approved