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.

A240918 Primes p such that p +/- product_of_digits(p) are both semiprimes.

Original entry on oeis.org

211, 257, 269, 461, 463, 467, 523, 547, 769, 829, 839, 947, 967, 983, 1129, 1213, 1259, 1327, 1361, 1381, 1429, 1433, 1453, 1487, 1619, 1667, 1721, 1723, 1741, 1811, 1847, 2143, 2153, 2161, 2243, 2251, 2311, 2339, 2357, 2371, 2473, 2531, 2591, 2593, 2617, 2659
Offset: 1

Views

Author

K. D. Bajpai, Aug 02 2014

Keywords

Examples

			211 is in the sequence because it is prime, and because 211 + (2 * 1 * 1) = 213 = 3 * 71 and 211 - (2 * 1 * 1) = 209 = 11 * 19 both are semiprimes.
461 is in the sequence because it is prime, and because 461 + (4 * 6 * 1) = 485 = 5 * 97 and 461 - (4 * 6 * 1) = 437 = 19 * 23 both are semiprimes.
		

Crossrefs

Programs

  • Mathematica
    Select[Prime[Range[500]], PrimeOmega[(Times @@ IntegerDigits[#] + #)] == 2 && PrimeOmega[(Times @@ IntegerDigits[#] - #)] == 2 &]
  • PARI
    forprime(p=10,10^4,d=digits(p);pp=prod(i=1,#d,d[i]);if(bigomega(p+pp)==2&&bigomega(p-pp)==2,print1(p,", "))) \\ Derek Orr, Aug 02 2014