A078499 Two-prime decades.

20, 30, 50, 60, 80, 150, 160, 170, 230, 250, 260, 270, 280, 330, 340, 350, 370, 380, 400, 440, 490, 500, 520, 540, 560, 570, 590, 600, 650, 670, 700, 730, 750, 760, 910, 940, 970, 990, 1010, 1100, 1120, 1150, 1180, 1210, 1220, 1230, 1270, 1280, 1290, 1320

Offset

1,1

Links

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

Maple

select(t -> nops(select(isprime, [t+1, t+3, t+7, t+9]))=2, [seq(i, i=10..10^4, 10)]); # Robert Israel, Feb 05 2019

Prog

(PARI) decade2(n1, n2) = { if(n1==0, n1=10); forstep(x=n1, n2, 10, if(isprime(x+1) && isprime(x+3) && !isprime(x+7) && !isprime(x+9), print1(x" "); ); if(isprime(x+1) && isprime(x+7) && !isprime(x+3) && !isprime(x+9), print1(x" "); ); if(isprime(x+1) && isprime(x+9) && !isprime(x+3) && !isprime(x+7), print1(x" "); ); if(isprime(x+3) && isprime(x+7) && !isprime(x+1) && !isprime(x+9), print1(x" "); ); if(isprime(x+3) && isprime(x+9) && !isprime(x+1) && !isprime(x+7), print1(x" "); ); if(isprime(x+7) && isprime(x+9) && !isprime(x+1) && !isprime(x+3), print1(x" "); ); ); }

Crossrefs

Sequence in context: A198471 A120145 A104048 * A066027 A256227 A142342

Adjacent sequences: A078496 A078497 A078498 * A078500 A078501 A078502

Keyword

easy,nonn,base

Author

Cino Hilliard, Jan 04 2003

Extensions

Offset corrected by Robert Israel, Feb 05 2019

Status

approved