A078492 No-prime decades.

200, 320, 510, 530, 620, 840, 890, 1070, 1130, 1140, 1260, 1330, 1340, 1350, 1410, 1460, 1500, 1640, 1670, 1680, 1710, 1760, 1790, 1850, 1890, 1920, 1960, 2040, 2070, 2100, 2180, 2190, 2320, 2360, 2400, 2480, 2490, 2510, 2560, 2580, 2820, 2940, 2980

Offset

0,1

Comments

Numbers n = 10*m such that none of n + 1, n + 3, n + 7, n + 9 are prime.

It is often possible to change the base 10 representation of a composite number into the representation of a prime by changing a single digit. That's not possible for the numbers in this sequence. - Alonso del Arte, Aug 25 2017

Links

Daniel Starodubtsev, Table of n, a(n) for n = 0..10000

Example

Given that 201 = 3 * 67, 203 = 7 * 29, 207 = 3^2 * 23, 209 = 11 * 19, we conclude that 200 is in the sequence.
210 is not in the sequence because 211 is prime.

Mathematica

Select[10Range[500], NextPrime[#] - # > 10 &] (* Alonso del Arte, Aug 25 2017 *)
Select[10 Range[300], NoneTrue[#+{1, 3, 7, 9}, PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 28 2020 *)

Prog

(PARI) decadenopr(n1, n2) = { forstep(x=n1, n2, 10, if(!isprime(x+1) && !isprime(x+3) && !isprime(x+7) && !isprime(x+9), print1(x", "); ); ); }
(Magma) [10*n: n in [0..300] | forall{i: i in [1, 3, 7, 9] | not IsPrime(10*n+i)}]; // Bruno Berselli, Jun 17 2016

Crossrefs

Sequence in context: A118118 A124472 A247399 * A166256 A252059 A004966

Adjacent sequences: A078489 A078490 A078491 * A078493 A078494 A078495

Keyword

nonn,base,easy

Author

Cino Hilliard, Jan 04 2003

Status

approved