1. a=2^25+2^26+2^27+2^28 =
=2^25×(1+2^1+2^2+2^3) =
=2^25×(1+2+4+8) =
=2^25×15 deci este divizibil cu 15
2. b=2^180+2^178+2^177+2^176=
= 2^176×(2^4+2^2+2^1+1)=
= 2^176×(16+4+2+1)=
= 2^176×23 deci este divizibil cu 23
3. c=2^999+2^998+2^997+2^996+2^995=
=2^995×(2^4+2^3+2^2+2^1+1)=
=2^995×(16+8+4+2+1)=
=2^995×31 deci este divizibil cu 31
4. d=2^18+2^20+2^22+2^24=
=2^18×(1+2^2+2^4+2^6)=
=2^18×(1+4+16+64)=
=2^18×85=
=2^18×5×17 deci este divizibil cu 17