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 A246857 #19 Sep 08 2022 08:46:09 %S A246857 2,3,5,11,23,29,41,53,83,89,113,131,173,179,191,233,239,251,281,293, %T A246857 329,359,413,419,431,443,491,509,593,623,641,653,659,683,719,743,761, %U A246857 809,869,911,953,979,1013,1019,1031,1049,1103,1223,1229,1289,1409,1439,1451 %N A246857 Numbers k such that sigma(k + sigma(k)) = 2*sigma(k). %C A246857 Union of A005384 (Sophie Germain primes) and A246858. %C A246857 First composite number in sequence is 329 (see A246858). %e A246857 Composite number 329 (with sigma(329) = 384) is in sequence because sigma(329+sigma(329)) = sigma(713) = 768 = 2*384. %e A246857 Prime 359 (with sigma(359) = 360) is in sequence because sigma(359+sigma(359)) = sigma(719) = 720 = 2*360. %t A246857 Select[Range[1500], DivisorSigma[1, # + DivisorSigma[1, #]] == 2 DivisorSigma[1, #] &] (* _Michael De Vlieger_, Aug 05 2021 *) %o A246857 (Magma) [n:n in[1..10000] | SumOfDivisors(n+SumOfDivisors(n)) eq 2*SumOfDivisors(n)] %o A246857 (PARI) select(n -> sigma(n+sigma(n))==2*sigma(n),[1..1000]) \\ _Edward Jiang_, Sep 05 2014 %Y A246857 Cf. A074400, A246456. %Y A246857 Cf. A005384, A246858. %K A246857 nonn %O A246857 1,1 %A A246857 _Jaroslav Krizek_, Sep 05 2014