Strange numbers
n is a strange number if every adjacent digit differs from its neighbour by prime number.
Let 100<n<500
Pascal
simple brute force, by adding a prime difference from digit to digit. <lang pascal>program strangenumbers; type
tDeltaIdx = 0..7;
const
dgtCnt = 3; deltaprime : array[tDeltaIdx] of Int32 =(-7,-5,-3,-2,2,3,5,7);
//globals are set to 0 var
Digits : array[0..dgtCnt-1] of Int32; Actdgt,i,j,k,Cnt : Int32;
procedure OutPut; Begin
write(Digits[0],Digits[1],Digits[2],' ');
end;
Begin
For i := 1 to 4 do Begin Digits[0] := i; For k in tDeltaIdx do Begin if (i+deltaprime[k]) in [0..9] then Begin Actdgt := i+deltaprime[k]; Digits[1]:= Actdgt; For j in tDeltaIdx do if (Actdgt+deltaprime[j]) in [0..9] then Begin Digits[2]:= Actdgt+deltaprime[j]; OutPut; inc(cnt); If cnt MOD 20 = 0 then writeln; end; end; end; end; writeln; Writeln('Count : ',cnt);
end. </lang>
- Output:
130 131 135 136 138 141 142 146 147 149 161 163 164 168 169 181 183 185 186 202 203 205 207 241 242 246 247 249 250 252 253 257 258 270 272 274 275 279 292 294 296 297 302 303 305 307 313 314 316 318 350 352 353 357 358 361 363 364 368 369 381 383 385 386 413 414 416 418 420 424 425 427 429 461 463 464 468 469 470 472 474 475 479 492 494 496 497 Count : 87
Raku
<lang perl6># 20210222 Raku programming solution
sub infix:<′>(\x,\y) { abs(x -y) ∈ [2, 3, 5, 7] ?? True !! False }
for (101..499) { .say if so all .comb.rotor(2 => -1).map: { @_[0] ′ @_[1] } }</lang>
- Output:
./strange.raku | wc 87 87 348
Ring
<lang ring> load "stdlib.ring"
row = 0 see "Strange numbers are:"
for n = 100 to 500
flag = 1 str = string(n) for m = 1 to len(str)-1 num1 = number(str[m]) num2 = number(str[m+1]) pr = fabs(num1-num2) if not isprime(pr) flag = 0 exit ok next if flag = 1 row = row + 1 if (row-1) % 11 = 0 see nl else see " " + str ok ok
next </lang>
- Output:
Strange numbers are: 131 135 136 138 141 142 146 147 149 161 164 168 169 181 183 185 186 202 203 205 241 242 246 247 249 250 252 253 257 258 272 274 275 279 292 294 296 297 302 303 307 313 314 316 318 350 352 353 357 358 363 364 368 369 381 383 385 386 413 414 418 420 424 425 427 429 461 463 464 468 470 472 474 475 479 492 494 496 497
Wren
<lang ecmascript>var primes = [2, 3, 5, 7] var count = 0 var d = [] System.print("Strange numbers in the open interval (100, 500) are:\n") for (i in 101..499) {
d.clear() var j = i while (j > 0) { d.add(j % 10) j = (j/10).floor } if (primes.contains((d[0] - d[1]).abs) && primes.contains((d[1] - d[2]).abs)) { System.write("%(i) ") count = count + 1 if (count % 10 == 0) System.print() }
} if (count % 10 != 0) System.print() System.print("\n%(count) strange numbers in all.")</lang>
- Output:
Strange numbers in the open interval (100, 500) are: 130 131 135 136 138 141 142 146 147 149 161 163 164 168 169 181 183 185 186 202 203 205 207 241 242 246 247 249 250 252 253 257 258 270 272 274 275 279 292 294 296 297 302 303 305 307 313 314 316 318 350 352 353 357 358 361 363 364 368 369 381 383 385 386 413 414 416 418 420 424 425 427 429 461 463 464 468 469 470 472 474 475 479 492 494 496 497 87 strange numbers in all.