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A189977
Primes p such that d(p+1) = 2*d(p-1), where d(k) counts the divisors of k.
2
2, 23, 149, 293, 311, 439, 557, 569, 743, 773, 857, 1031, 1151, 1493, 1607, 1663, 1709, 1733, 1879, 1913, 2069, 2141, 2423, 2711, 2719, 2729, 2789, 2969, 3191, 3209, 3559, 3607, 3767, 3821, 3833, 3847, 3929, 3967, 4019, 4073, 4229, 4339, 4451, 4517, 4549
OFFSET
1,1
LINKS
MATHEMATICA
Select[Prime[Range[PrimePi[5059]]], 2*DivisorSigma[0, # - 1] == DivisorSigma[0, # + 1] &] (* T. D. Noe, May 03 2011 *)
PROG
(PARI) isok(p) = isprime(p) && (numdiv(p+1) == 2*numdiv(p-1)); \\ Michel Marcus, Jan 13 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Ctibor O. Zizka, May 03 2011
STATUS
approved