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 A078403 #16 May 14 2025 14:51:18 %S A078403 2,3,5,7,11,23,29,41,43,47,59,61,79,83,97,101,113,131,137,149,151,167, %T A078403 173,191,223,227,239,241,257,263,277,281,293,311,313,317,331,347,349, %U A078403 353,367,383,389,401,419,421,439,443,457,461,479,491,509,547,563,569 %N A078403 Primes whose digital root (A038194) is prime. %C A078403 Union of A061238, A061240, A061241 and 3. - _Ya-Ping Lu_, Jan 03 2024 %F A078403 a(n) ~ 2n log n. - _Charles R Greathouse IV_, May 14 2025 %e A078403 59 is a term because 5+9=14, giving (final) iterated sum 1+4=5 and 5 is prime. %t A078403 Select[ Range[580], PrimeQ[ # ] && PrimeQ[Mod[ #, 9]] &] %t A078403 Select[Prime[Range[200]],PrimeQ[Mod[#,9]]&] (* _Harvey P. Dale_, Aug 20 2017 *) %o A078403 (PARI) forprime(p=2,997,if(isprime(p%9),print1(p,","))) %o A078403 (Python) from sympy import isprime, primerange; [print(p, end = ', ') for p in primerange(2, 570) if isprime(p%9)] # _Ya-Ping Lu_, Jan 03 2024 %Y A078403 Cf. A038194, A061238, A061240, A061241, A070027, A078400. %K A078403 base,easy,nonn %O A078403 1,1 %A A078403 _N. J. A. Sloane_, Dec 26 2002 %E A078403 Extended by _Robert G. Wilson v_, _Klaus Brockhaus_ and _Rick L. Shepherd_, Dec 27 2002