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 A290425 #21 Jan 17 2024 09:20:02 %S A290425 23,233,2333,23333 %N A290425 Primes p such that the reverse of 4*p is the nextprime(p+1). %C A290425 From _David A. Corneth_, Aug 02 2017: (Start) %C A290425 23333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333 is a term. %C A290425 Terms start with 2 and end in 3. Proof (for base 10): %C A290425 Let d[1] be the first digit of term p. Then 1 <= d[1] <= 9. Let r be the reverse of 4*p. If d[1] > 2 then r is too large to be nextprime(p + 1). if p = 1 then 4*p starts with 5 or 6 i.e. r ends in 5 or 6. No terms can match these conditions so d[1] = 2. If d[1] = 2 then p ends in 3 or 8. As primes don't end in 8, p ends in 3. (End) %e A290425 p(9)=23, 4*23=92; 29=p(10). %t A290425 Select[Prime@ Range[10^6], NextPrime@ # == IntegerReverse[4 #] &] (* _Michael De Vlieger_, Aug 02 2017 *) %o A290425 (PARI) is(n) = isprime(n) && fromdigits(Vecrev(digits(4*n))) == nextprime(n+1) \\ _David A. Corneth_, Aug 02 2017 %Y A290425 Cf. A093672, A198972. %K A290425 nonn,base,more %O A290425 1,1 %A A290425 _David James Sycamore_, Jul 31 2017