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A078492 No-prime decades. 2
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 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=0..42.

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 *)

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

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Last modified October 16 23:46 EDT 2019. Contains 328103 sequences. (Running on oeis4.)