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 A366826 #19 Nov 19 2023 02:04:52 %S A366826 4,6,8,9,22,25,27,32,33,35,52,55,57,72,75,77,237,537,737 %N A366826 Composite numbers whose proper substrings (of their decimal expansions) are all primes. %C A366826 There are no terms greater than 999 because the only three-digit prime whose substrings are all primes is 373 (see A085823) and prepending or appending any prime digit to it would create a different three-digit substring. %e A366826 237 is included because it is composite and 2, 3, 7, 23 and 37 are all primes. %e A366826 4 is included because it is composite and has no proper substrings. %o A366826 (Python) %o A366826 from itertools import combinations %o A366826 from sympy import isprime %o A366826 for n in range(2, 1000): %o A366826 if not isprime(n): %o A366826 properSubstrings = set( %o A366826 int(str(n)[start:end]) for (start, end) %o A366826 in combinations(range(len(str(n)) + 1), 2) %o A366826 ) - set((n,)) %o A366826 if all(isprime(s) for s in properSubstrings): %o A366826 print(n, end=', ') %Y A366826 Subsequence of A002808. %Y A366826 Cf. A000040. %Y A366826 Cf. A061371, A062115, A202262. %Y A366826 Cf. A033274, A068669, A085823, A279366. %K A366826 base,fini,full,nonn %O A366826 1,1 %A A366826 _Kalle Siukola_, Oct 25 2023