A119705
Primes p such that the number of divisors of p+1 equals number of divisors of p+2.
Original entry on oeis.org
13, 37, 43, 97, 103, 157, 229, 241, 331, 373, 433, 541, 547, 877, 907, 1021, 1129, 1201, 1373, 1381, 1433, 1489, 1543, 1597, 1613, 1621, 1741, 1831, 1951, 1987, 2017, 2053, 2161, 2377, 2503, 2539, 2557, 2633, 2677, 2713, 2857, 2953, 3061, 3067, 3109, 3169
Offset: 1
13 is a term because 14 and 15 each have 4 divisors: {1, 2, 7, 14} and {1, 3, 5, 15}.
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Select[Range[3200], PrimeQ[#] && DivisorSigma[0, # + 1] == DivisorSigma[0, # + 2] &] (* Amiram Eldar, Jan 26 2020 *)
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isok(n) = isprime(n) && (numdiv(n+1) == numdiv(n+2)); \\ Michel Marcus, Oct 10 2013
A119728
Primes p such that p+1, p+2, p+3 and p+4 have equal number of divisors.
Original entry on oeis.org
241, 13781, 19141, 21493, 50581, 61141, 76261, 77431, 94261, 95383, 95413, 98101, 104743, 104869, 134581, 141653, 142453, 152629, 153991, 158341, 160933, 165541, 169111, 199831, 201511, 203431, 206551, 229351, 233941, 235111, 253013, 273367
Offset: 1
241 is a term since 242, 243, 244 and 245 all have 6 divisors:
{1,2,11,22,121,242},{1,3,9,27,81,243},{1,2,4,61,122,244} and {1,5,7,35,49,245}.
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Select[Prime@Range@50000,DivisorSigma[0,#+1]==DivisorSigma[0,#+2]==DivisorSigma[0,#+3]==DivisorSigma[0,#+4]&]
A119740
Primes p such that p+1, p+2, p+3, p+4, p+5 and p+6 have equal number of divisors.
Original entry on oeis.org
298693, 346501, 1841141, 2192933, 2861461, 3106981, 3375781, 3435589, 3437813, 3865429, 4597013, 6191461, 7016213, 7074901, 7637941, 7918373, 9196309, 10216901, 12798901, 13747429, 14100661, 14171653, 14770981, 14779189
Offset: 1
298693 is a term since 298694, 298695, 298696, 298697, 298698 and 298699 all have 8 divisors:
{1,2,11,22,13577,27154,149347,298694}, {1,3,5,15,19913,59739,99565,298695},
{1,2,4,8,37337,74674,149348,298696}, {1,7,71,497,601,4207,42671,298697},
{1,2,3,6,49783,99566,149349,298698}, {1,19,79,199,1501,3781,15721,298699}.
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Select[Prime@Range[1000000],DivisorSigma[0,#+1]==DivisorSigma[0,#+2]==DivisorSigma[0,#+3]==DivisorSigma[0,#+4]==DivisorSigma[0,#+5]==DivisorSigma[0,#+6]&]
Showing 1-3 of 3 results.
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