#include <Arduino.h>

#define R1 23
#define R2 22
#define R3 21
#define BTN2 26

int seq1[] = {R1};
int seq2[] = {R1, R2, R3};

void setup() {
  pinMode(R1, OUTPUT);
  pinMode(R2, OUTPUT);
  pinMode(R3, OUTPUT);

  pinMode(BTN2, INPUT_PULLUP);
}

void blinkSeq(int seq[], int n) {
  for (int i = 0; i < n; i++) {
    digitalWrite(seq[i], HIGH);
    delay(500);
    digitalWrite(seq[i], LOW);
    delay(500);
  }
}

void loop() {
  if (digitalRead(BTN2) == LOW) blinkSeq(seq2, 3);
}