A145985 Primes resulting from subtracting primes from 10^n in order (see Comments for precise definition).

7, 5, 3, 89, 83, 71, 59, 53, 47, 41, 29, 17, 11, 3, 887, 863, 827, 821, 809, 773, 761, 743, 719, 683, 653, 647, 641, 617, 599, 569, 557, 521, 509, 491, 479, 443, 431, 401, 383, 359, 353, 347, 317, 281, 257, 239, 227, 191, 179, 173, 137, 113, 89, 71, 59, 53, 47, 29, 23, 17, 3, 8969, 8951, 8849, 8837, 8819, 8807, 8783

Offset

1,1

Comments

Comments from N. J. A. Sloane, Dec 18 2022 (Start)

A more precise definition is the following.

Start with k=1; let N=10^k, let i run from 10^(k-1)-1 to N-1, let j = N-i, if i and j are both primes, append j to the sequence; increment k.

This is derived from A068811 via a(n) = 10^d - A068811(n) where d is the number of digits in A068811(n). A068811 is more fundamental, for there the primes appear in order and there are no duplicates. (End)

Primes may appear more than once.

Links

N. J. A. Sloane, Table of n, a(n) for n = 1..20000 [First 1000 terms from Harvey P. Dale]

N. J. A. Sloane, Table of n, a(n) for n = 1..80338

Example

887 is a term because 1000-887 = 113 and both 887 and 113 are prime.

Maple

a:=[];
for k from 1 to 6 do
N := 10^k;
   for i from 10^(k-1)+1 to N-1 do
      j:=N-i;
      if isprime(i) and isprime(j) then a:=[op(a), j]; fi;
   od:
od;
a; # N. J. A. Sloane, Dec 16 2022

Mathematica

Select[Table[10^IntegerLength[p]-p, {p, Prime[Range[200]]}], PrimeQ] (* Harvey P. Dale, Dec 16 2022 *)

Crossrefs

Cf. A068811, A358310, A359121, A359122, A359123.

See A359120 for the length of the n-th block of decreasing terms.

Sequence in context: A144846 A090289 A160670 * A109863 A179177 A021574

Adjacent sequences: A145982 A145983 A145984 * A145986 A145987 A145988

Keyword

easy,nonn

Author

Enoch Haga, Oct 27 2008

Extensions

Corrected and edited by Harvey P. Dale and N. J. A. Sloane, Dec 16 2022

Status

approved