The 555 has 8 pins...
network electronics
40 PINS
Originally designed as a timer it has dozens of possible uses:timerflipfloppulse width modulatorpulse position modulatoretc.
The 7805 regulator IC has three pins; input, output, and ground. The case is also a pin, but it is grounded, so there are still only three pins, for all practical purposes.
8-pin 555 timer IC
it have 40 pins 1st one is ground and last one is Vcc. Itplh = 450
for simplicity of calculation of no of pins
IC pins are numbered anti-clockwise around the IC starting near the notch or dot.
these two pins are biasing pins of ICs.
IC's which starts from 7 are most of them are digital ic's . not all the IC's starts with 7 for example LM380 audio IC CTC810 audio amplifier ic and lm317 voltage regulator ic ,NE555 timer ic, 4017 counter and so other. there are no fact behind them . 7400- nand 7402 -nor 7404-not 7408-and 7432-or 7486-exor 74266-ex-nor 74147 priority encoder.
The non-inverting pins of the LM393 are 3 and 5.
to avoid floating pins ...........so as to avoid rail to rail current