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.

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A125841 Numbers k such that previous_prime(k)=k-sd and next_prime(k)=k+sd where sd is sum of the distinct prime factors of k.

Original entry on oeis.org

144, 288, 1728, 5184, 7168, 11760, 21632, 21952, 73500, 110592, 113400, 114244, 151263, 153790, 186624, 205800, 235298, 250563, 663552, 708588, 1404928, 2976750, 3449628, 4738500, 5265000, 7077888, 9437184, 11529602, 11745162
Offset: 1

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Author

Farideh Firoozbakht, Feb 04 2007, corrected Feb 08 2007

Keywords

Comments

14267656658790241528591830756844692582808594415616 is a 50-digit term of this sequence. 493009335 is the smallest number k such that previous_prime(k)=k-s and next_prime(k)=k+s where s is sum of the prime factors of k. What is the next number with the same property?

Examples

			113400=2^3*3^4*5^2*7 is a term because previous_prime(113400)=113400-(2+3+5+7) and next_prime(113400)=113400+(2+3+5+7).

Crossrefs

Cf. A008472, A125840.

Programs

  • Mathematica
    Do[If[c=Apply[Plus,PrimeFactorList[n]];n-c==PreviousPrime[n]&&n+c== NextPrime[n],Print[n]],{n,4,20000000}]
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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