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A108841 Palindromic primes in which all internal digits are 4. 1
1444441, 3444443, 74444444447, 3444444444443, 7444444444444444444444444444447, 1444444444444444444444444444444444444444444444444444444444444444441 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The next term has 121 digits. - Harvey P. Dale, Nov 26 2014

a(10) has 1255 digits, and thus is too big for a b-file. - Robert Israel, Oct 25 2018

LINKS

Robert Israel, Table of n, a(n) for n = 1..9

MAPLE

select(isprime, [seq(seq(x*(10^d+1)+40*(10^(d-1)-1)/9, x=1..9, 2), d=2..66)]); # Robert Israel, Oct 25 2018

MATHEMATICA

Sort[Select[FromDigits/@Flatten[Table[Join[{n}, PadRight[{}, i, 4], {n}], {n, {1, 3, 7, 9}}, {i, 150}], 1], PrimeQ]] (* Harvey P. Dale, Nov 26 2014 *)

PROG

(PARI) n10np1(n, d) = { local(x, y, k); for(x=1, n, for(k=1, 8, y=10^(x+1)*k+floor(10^x*d/9)*10+k; if(isprime(y), print1(y", ")) ) ) }

CROSSREFS

Sequence in context: A259306 A210629 A156621 * A124490 A124491 A205892

Adjacent sequences:  A108838 A108839 A108840 * A108842 A108843 A108844

KEYWORD

nonn,base

AUTHOR

Cino Hilliard, Jul 11 2005

EXTENSIONS

Name changed by Arkadiusz Wesolowski, Sep 07 2011

STATUS

approved

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Last modified January 27 10:55 EST 2022. Contains 350607 sequences. (Running on oeis4.)