cp's OEIS Frontend

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.

A347422 Numbers k such that the product of the number of divisors of k and the number of pairs of primes summing to k is k itself.

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%I A347422 #69 Sep 24 2021 03:14:59
%S A347422 24,36,72,1056,1176,11232,226080
%N A347422 Numbers k such that the product of the number of divisors of k and the number of pairs of primes summing to k is k itself.
%C A347422 All terms are even.
%C A347422 a(8) >= 3.5*10^6. - _David A. Corneth_, Sep 02 2021
%C A347422 a(8) >= 5*10^6. - _Michel Marcus_, Sep 10 2021
%C A347422 a(8) > 2.5*10^8. - _Martin Ehrenstein_, Sep 23 2021
%H A347422 Anudeex Shetty, <a href="/A347422/a347422.txt">Python program for A347422</a>
%e A347422 For 24, the number of divisors is 8 (1, 2, 3, 4, 6, 8, 12, 24), the number of pairs of prime numbers summing to 24 is 3: (5, 19), (7, 17), (11, 13), and 3*8=24, so 24 is a term.
%e A347422 Similarly, for 226080, the number of divisors is 72, and the number of pairs of prime numbers summing to 226080 is 3140. And 72*3140 = 226080, so 226080 is a term.
%t A347422 Select[Range[12000], IntegerQ[(r = #/DivisorSigma[0, #])] && r == Length @ IntegerPartitions[#, {2}, Select[Range[#], PrimeQ]] &] (* _Amiram Eldar_, Sep 02 2021 *)
%o A347422 (PARI) f(n) = my(s); forprime(q=2, n\2, s+=isprime(n-q)); s; \\ A061358
%o A347422 isok(k) = my(x = k/numdiv(k)); (denominator(x)==1) && (f(k) == x); \\ _Michel Marcus_, Sep 10 2021
%Y A347422 Cf. A000005, A061358.
%Y A347422 Subsequence of A033950.
%K A347422 nonn,hard,more,less
%O A347422 1,1
%A A347422 _Anudeex Shetty_ and _Nivesh Raj_, Sep 02 2021