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.

A331099 The numbers such that the sum of their proper divisors plus the product of their digits equals the number.

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%I A331099 #23 Sep 08 2022 08:46:24
%S A331099 1,14,27,154,284,574,1264,2588,7288,49852,2342656,33550336,8589869056
%N A331099 The numbers such that the sum of their proper divisors plus the product of their digits equals the number.
%C A331099 The perfect numbers containing a 0 digit are all in this sequence.
%C A331099 a(14) > 10^13. - _Giovanni Resta_, Jan 19 2020
%e A331099 14 is a term as A001065(14) = 10, A007954(14) = 4, and 10 + 4 = 14.
%e A331099 2588 is a term as A001065(2588) = 1948, A007954(2588) = 640, and 1948 + 640 = 2588.
%t A331099 Select[Range[10^6], DivisorSigma[1, #] + Times @@ IntegerDigits[#] == 2 # &] (* _Amiram Eldar_, Jan 18 2020 *)
%o A331099 (Magma) [k:k in [1..2500000]| k eq &*Intseq(k)+DivisorSigma(1,k)-k]; // _Marius A. Burtea_, Jan 18 2020
%o A331099 (PARI) isok(n) = my(d=digits(n)); sigma(n) + vecprod(d) == 2*n; \\ _Jinyuan Wang_, Jan 19 2020
%Y A331099 Cf. A001065, A007954, A331098.
%K A331099 nonn,base,less,more
%O A331099 1,2
%A A331099 _Scott R. Shannon_, Jan 09 2020
%E A331099 a(12) from _Jinyuan Wang_, Jan 19 2020
%E A331099 a(13) from _Giovanni Resta_, Jan 19 2020