C (gcc), 65 bytes

i;main(c){for(i=c;i--+2;)printf("%d",2-!(i-c+1&&i+2));main(c+2);} 

Infinitely prints the sequence.

-1 byte thanks to RGS!

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C (gcc), 56 bytes

i,c;main(){main(i--<-2?i=c+=2:putchar(49+(c+~i&&i+3)));} 

-1 byte thanks to RGS!
-8 bytes thanks to ceilingcat!

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C (gcc), 46 bytes

i;f(n){for(i=0;n--;)printf("%d",i=i*100+121);} 

Stretches the rules and only works up to \$n=4\$.

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C (gcc), 68 66 bytes

i;main(c){for(i=c;i--+2;)printf("%d ",2-!(i-c+1&&i+2));main(c+2);} 

Infinitely prints the sequence.

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C (gcc), 65 bytes

i;main(c){for(i=c;i--+2;)printf("%d",2-!(i-c+1&&i+2));main(c+2);} 

Infinitely prints the sequence.

-1 byte thanks to RGS!

Try it online!

C (gcc), 68 bytes

f(c,i){for(c=0;;c++)for(i=++c;i--+2;)printf("%d ",2-!(i-c+1&&i+2));} 

Same as my solution to the other question but without the boilerplate.

Infinitely prints the sequence.

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C (gcc), 68 66 bytes

i;main(c){for(i=c;i--+2;)printf("%d ",2-!(i-c+1&&i+2));main(c+2);} 

Infinitely prints the sequence.

Try it online!