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 A078782 #11 Nov 14 2024 08:20:32 %S A078782 4,6,9,12,18,21,26,28,34,42,45,52,57,60,65,74,81,84,91,95,98,106,112, %T A078782 119,128,133,135,141,143,147,165,170,177,180,192,195,203,209,214,220, %U A078782 228,231,244,246,250,253,267,284,288,290,295,301,303,316,323,329,336 %N A078782 Nonprimes (A018252) with prime (A000040) subscripts. %C A078782 a(n) = A018252(A000040(n)). Subsequence of A175250 (nonprimes (A018252) with noncomposite (A008578) subscripts), a(n) = A175250(n+1). a(n) U A102615(n) = A018252(n). [From _Jaroslav Krizek_, Mar 13 2010] %e A078782 a(4) = nonprime(prime(4)) = nonprime(7) = 12. %o A078782 (Python) %o A078782 from sympy import prime, composite %o A078782 def A078782(n): return composite(prime(n)-1) # _Chai Wah Wu_, Nov 13 2024 %Y A078782 Let A = primes A000040, B = nonprimes A018252. The 2-level compounds are AA = A006450, AB = A007821, BA = A078782, BB = A102615. The 3-level compounds AAA, AAB, ..., BBB are A038580, A049078, A270792, A102617, A270794, A270796, A102216. %K A078782 easy,nonn %O A078782 1,1 %A A078782 _Joseph L. Pe_, Jan 09 2003 %E A078782 Corrected by _Jaroslav Krizek_, Mar 13 2010