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A051835 Palindromic Sophie Germain primes. 2
2, 3, 5, 11, 131, 191, 12821, 14741, 19391, 19991, 36563, 38183, 93239, 96269, 1028201, 1074701, 1150511, 1178711, 1243421, 1281821, 1317131, 1333331, 1407041, 1456541, 1508051, 1532351, 1557551, 1598951, 1600061, 1609061 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

p and 2p+1 are primes (cf. A005384) and p is a palindrome.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

H. Dubner, Palindromic Sophie Germain primes, Journal of Recreational Mathematics, Vol. 26, No. 1, pp. 38-41, 1994.

MAPLE

makepali:= proc(n, d) local L; # case with d odd

  L:= convert(n, base, 10);

  10^((d-1)/2)*n + add(L[i]*10^((d+1)/2-i), i=2..(d+1)/2)

end proc:

N:= 100: # for a(1)..a(N)

R:= 2, 3, 5, 11: count:= 4:

for d from 3 by 2  while count < N do

  for i in [1, 3, 7, 9] while count < N do

    for x from 0 to 10^((d-1)/2)-1 while count < N do

      y:= makepali(i*10^((d-1)/2)+x, d);

      if isprime(y) and isprime(2*y+1) then

        R:= R, y;

        count:= count+1;

       fi

od od od:

R; # Robert Israel, Nov 22 2020

CROSSREFS

Cf. A002385, A005384.

Sequence in context: A117701 A056163 A118573 * A075883 A195815 A327428

Adjacent sequences:  A051832 A051833 A051834 * A051836 A051837 A051838

KEYWORD

base,nonn

AUTHOR

Warut Roonguthai Dec 11 1999

STATUS

approved

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Last modified March 3 14:58 EST 2021. Contains 341762 sequences. (Running on oeis4.)