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A375777
Numbers k such that k - rad(k) - 1 is prime, where rad(k) is A007947(k).
0
8, 9, 12, 16, 18, 24, 25, 27, 28, 32, 36, 40, 45, 48, 49, 54, 56, 60, 63, 64, 75, 76, 84, 90, 96, 98, 100, 108, 112, 120, 121, 124, 126, 136, 144, 148, 152, 153, 160, 171, 175, 180, 184, 189, 196, 198, 204, 207, 208, 220, 228, 232, 243, 250, 261, 264, 270, 276
OFFSET
1,1
EXAMPLE
12 is a term, because 12 - rad(12) - 1 = 12 - (2 * 3) - 1 = 12 - 6 - 1 = 5 is prime.
MATHEMATICA
Select[Range[300], PrimeQ[# - Times @@ FactorInteger[#][[;; , 1]] - 1] &] (* Amiram Eldar, Aug 27 2024 *)
PROG
(PARI) isok(k) = isprime(k - (vecprod(factor(k)[, 1])) - 1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Arsen Vardanyan, Aug 27 2024
STATUS
approved