Python
По заданной последовательности a1, a2, …, an чисел вычислите сумму a1∗a2+a2∗a3+⋯+an−1∗an.

def series(n):

summa=0

if (n>=2) and (n<=100):

 for i in range(2, n):

  print(i)

  summa=summa+(i)*(i+1)

 print(summa)

else:

 print("Неверные вводные данные")

var i,s,p: integer; a: array [1..100] of integer;

begin 

s: =0; p: =0;

writeln('vvedite masiv a: ');  

for i: =1 to 10 do begin

write('a[',i,']=');

readln(a[i]);

end;

for i: =1 to 10 do begin

if a[i]> 0 then s: =s+a[i];  

end;

s: =s*2;

writeln('udvoennaya suma polozhitelnih elementov=',s);

writeln('indexi elementov kotorie bolshe prediduschego: ');

writeln;

for i: =2 to 10 do begin

if a[i]> a[i-1] then write(i,', ');

end;

for i: =2 to 10 do begin

if ((a[i]> =0) and (a[i-1]> =0)) or ((a[i]< 0) and (a[i-1]< 0)) then p: =p+1;

end;

writeln;

if p> 0 then writeln('masiv imeet pari sosednih elementov s odnakovimi znakami') else   writeln('masiv ne imeet pari sosednih elementov s odnakovimi znakami');  

readln(s);

end. 

if(a> b) cout < < a;

if(a< b)cout < < b;