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 A158641 #17 Jun 02 2025 01:26:53
%S A158641 3,5,11,17,41,107,137,347,2111,2657,3527,4421,6761,21011,24371,32057
%N A158641 Strong primes p: adding 2 to any one digit of p produces a prime number (no digits 8 & 9 in p).
%C A158641 All terms are lesser of twin pairs.
%C A158641 The sequence is finite. In particular, there are no terms longer than 5 digits since 2*10^k for k=0,1,...,5 give all nonzero residues modulo 7, implying that adding 2 to some digit yields a multiple of 7. - _Max Alekseyev_, Apr 25 2010
%e A158641 2111 is in this sequence because all 2111, 4111, 2311, 2131 and 2113 are prime numbers.
%e A158641 32057 is in this sequence because all 32057, 52057, 34057, 32257, 32077 and 32059 are prime numbers.
%p A158641 Lton := proc(L) local i; add(op(i,L)*10^(i-1),i=1..nops(L)) ; end: isA158641 := proc(p) local pdgs,pplus,i ; if isprime(p) then pdgs := convert(p,base,10) ; if convert(pdgs,set) intersect {8,9} <> {} then false; else for i from 1 to nops(pdgs) do pplus := subsop(i=2+op(i,pdgs),pdgs) ; if not isprime(Lton(pplus)) then RETURN(false); fi; od: true; fi; else false; fi; end: for n from 1 do p := ithprime(n) ; if isA158641(p) then print(p) ; fi; od: # _R. J. Mathar_, Apr 16 2009
%t A158641 spQ[p_]:=Max[IntegerDigits[p]]<8&&AllTrue[FromDigits/@Table[MapAt[ 2+#&,IntegerDigits[ p],n],{n,IntegerLength[p]}],PrimeQ]; Select[Prime[ Range[ 3500]],spQ] (* _Harvey P. Dale_, Nov 26 2022 *)
%o A158641 (PARI) test(p)=my(v=eval(Vec(Str(p)))); for(i=1,#v, if(v[i]>7,return(0))); for(i=0,#v-1, if(!isprime(p+2*10^i), return(0))); 1
%o A158641 forprime(p=2,4e9, if(isprime(p+2) && test(p), print1(p","))) \\ _Charles R Greathouse IV_, Sep 09 2009
%o A158641 (PARI) has(n)=if(vecmax(Set(digits(n)))>7, return(0)); for(i=0,#digits(n)-1, if(!isprime(n+2*10^i), return(0))); 1
%o A158641 select(has, primes(3438)) \\ _Charles R Greathouse IV_, Mar 11 2016
%Y A158641 Cf. A050249, A158124, A158125 Weakly prime numbers (changing any one digit always produces a composite number).
%K A158641 nonn,full,fini,base
%O A158641 1,1
%A A158641 _Zak Seidov_, Mar 23 2009
%E A158641 Keywords full, fini from _Max Alekseyev_, Apr 25 2010