This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A028842 #27 Jul 08 2025 18:54:03 %S A028842 2,3,5,7,12,13,15,17,21,31,51,71,112,113,115,117,121,131,151,171,211, %T A028842 311,511,711,1112,1113,1115,1117,1121,1131,1151,1171,1211,1311,1511, %U A028842 1711,2111,3111,5111,7111,11112,11113,11115,11117,11121,11131,11151 %N A028842 Numbers whose product of digits is prime. %H A028842 Vincenzo Librandi, <a href="/A028842/b028842.txt">Table of n, a(n) for n = 1..130</a> %H A028842 <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a> %t A028842 Select[Range[11160], PrimeQ[Times@@IntegerDigits[#]] &] (* _Jayanta Basu_, Jun 02 2013 *) %o A028842 (Sage) [x for x in range(10^5) if (prod(Integer(x).digits(base=10))) in Primes()] # _Bruno Berselli_, May 05 2014 %o A028842 (Scala) (1 to 10000).filter(n => List(2, 3, 5, 7).contains(n.toString.toCharArray.map(_ - 48).scanRight(1)(_ * _).head)) // _Alonso del Arte_, Apr 14 2020 %o A028842 (PARI) isok(n) = isprime(vecprod(digits(n))); \\ _Michel Marcus_, Apr 17 2020 %o A028842 (PARI) is(n)=my(d=digits(n),p); for(i=1,#d,if(d[i]==1,next); if(isprime(d[i]) && !p, p=1, return(0))); p \\ _Charles R Greathouse IV_, Apr 18 2020 %Y A028842 Cf. A007954, A028843, A028834, A046703 (subsequence of primes). %K A028842 nonn,base,easy %O A028842 1,1 %A A028842 _N. J. A. Sloane_ %E A028842 More terms from _Erich Friedman_. %E A028842 Name edited by _Jianing Song_, Jul 07 2025