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  1. #include <stdio.h>
  2. //a{n} = 2a{n-1} + a{n-2}, a{1}=2, a{2}=3(再帰なし版)
  3.  
  4. int main(void) {
  5. int n = 4;
  6. int a, b = 3, c = 2;
  7. for(int i = 3; i <= n; i++){
  8. a = 2*b + c;
  9. c = b;
  10. b = a;
  11. }
  12. printf("数列a%dの値は%d\n", n, a);
  13. return 0;
  14. }
  15.  
  16.  
Success #stdin #stdout 0.01s 5272KB
stdin
Standard input is empty
stdout
数列a4の値は19