#define t1  20
int nanoPin[16] = {
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  10,
  11,
  12,
  13,
  14,
  15,
  16,
  17
};
const int chCount = sizeof(nanoPin) / sizeof(nanoPin[0]);

// Global variables since they are used every time the loop is called
unsigned int stack = 0;
unsigned int chaser = chCount-1;

void setup() {
  for (int op=0; op < chCount; op++) {
    pinMode(nanoPin[op], OUTPUT);
    delay(10);
  }
}

void loop(){
  // Go throught the LEDs once per loop
  // Turn on the chaser LED, turn off all LEDs not already "stacked"
  for (unsigned int led=stack; led < chCount; led++) {
    if (led == chaser) {
      digitalWrite(nanoPin[led], HIGH);
    }
    else if (led != stack) {
      digitalWrite(nanoPin[led], LOW);
    }
  }

  // the delay
  delay(t1);

  // Move the chaser LED down the line
  chaser--;
  // Reset the chaser when hitting bottom
  if (chaser >= chCount) {
    chaser = chCount-1;

    // Increase the stack
    stack++;
    // Reset the stack when reaching top
    stack %= chCount;
  }
}