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A240918 Primes p such that p +/- product_of_digits(p) are both semiprimes. 1
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 (list; graph; refs; listen; history; text; internal format)
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 * A317394 A096706 A001583

Adjacent sequences:  A240915 A240916 A240917 * A240919 A240920 A240921

KEYWORD

nonn,base,less

AUTHOR

K. D. Bajpai, Aug 02 2014

STATUS

approved

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Last modified September 19 18:59 EDT 2020. Contains 337182 sequences. (Running on oeis4.)