#include lrblib.tc
#include pps/library.tc

[
multseq.tc - lrb - 9/14/13, 6/18/19

This program computes 3^n-3n

subtract computes the difference of a and b and puts it in a. It
destroys the contents of b. 9's complement arithmetic is used.
]

subtract int a(0),b(0),d [
 int i
 while i<=d [
  b(i)=9-b(i);i=i+1
  ]
 add a,b,d
 b(d)=1;i=0
 while i<d [
  b(i)=0;i=i+1
  ]
 add a,b,d
 ]

// add computes the sum of a and b and puts it in a.

add int a(0),b(0),d [
 int i,c,w
 while i<=d [
  w=a(d-i)+b(d-i)+c;a(d-i)=w%10;c=w/10;i=i+1
  ]
 ]

// multiply computes the product of m and a and puts it in a.

multiply int a(0),m,d [
 int i,c,w
 while i<=d [
  w=a(d-i)*m+c;a(d-i)=w%10;c=w/10;i=i+1
  ]
 ]

main [
 pl "multseq.tc - 6/18/19 - tct"
 int a(1000),b(1000),i,j,d,n
 printf "%c%center a number <= 2000: ",10,10;n=gn;pl ""
 d=(n+1)/2;a(d)=3
 while i<=n-2 [ // compute 3^n
  putchar '.';if ((i+1)%40==0) pl ""
  multiply a,3,d
  i=i+1
  ]
 i=0
 while n [
  b(d-i)=n%10;n=n/10
  i=i+1
  ]
 multiply b,3,d // b now holds 3n
 subtract a,b,d // compute 3^n-3n
 i=0;while (a(i)==0) i=i+1 // don't print leading 0's
 j=i;pl "";pl "The";pn d-i+1;ps " digit value is";pl "";putchar 7;sak;pl "";pl ""
 while i<=d [
  MC a(i),14
  i=i+1;if ((i-j)%40==0) pl ""
  ]
 pl ""
 ]