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

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

1,1

Links

K. D. Bajpai, Table of n, a(n) for n = 1..10460

Example

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.

Mathematica

Select[Prime[Range[500]], PrimeOmega[(Times @@ IntegerDigits[#] + #)] == 2 && PrimeOmega[(Times @@ IntegerDigits[#] - #)] == 2 &]

Prog

(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

Crossrefs

Cf. A000040, A001358, A227217.

Sequence in context: A031931 A246136 A087833 * A346948 A317394 A096706

Adjacent sequences: A240915 A240916 A240917 * A240919 A240920 A240921

Keyword

nonn,base,less

Author

K. D. Bajpai, Aug 02 2014

Status

approved