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A119730 Primes p such that p+1, p+2, p+3, p+4 and p+5 have equal number of divisors. 4
13781, 19141, 21493, 50581, 142453, 152629, 253013, 298693, 307253, 346501, 507781, 543061, 845381, 1079093, 1273781, 1354501, 1386901, 1492069, 1546261, 1661333, 1665061, 1841141, 2192933, 2208517, 2436341, 2453141, 2545013 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
13781 is a term since 13782, 13783, 13784, 13785 and 13786 all have 8 divisors:
{1,2,3,6,2297,4594,6891,13782}, {1,7,11,77,179,1253,1969,13783},
{1,2,4,8,1723,3446,6892,13784}, {1,3,5,15,919,2757,4595,13785} and
{1,2,61,113,122,226,6893,13786}.
MATHEMATICA
Select[Prime@Range[1000000], DivisorSigma[0, #+1]==DivisorSigma[0, #+2]==DivisorSigma[0, #+3]==DivisorSigma[0, #+4]==DivisorSigma[0, #+5]&]
endQ[n_]:= Length[Union[DivisorSigma[0, (n + Range[5])]]]==1; Select[Prime[ Range[ 200000]], endQ] (* Harvey P. Dale, Jan 16 2019 *)
CROSSREFS
Sequence in context: A235184 A270639 A031807 * A204839 A208487 A188102
KEYWORD
nonn
AUTHOR
Zak Seidov, Jul 29 2006
STATUS
approved

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Last modified February 22 01:50 EST 2024. Contains 370239 sequences. (Running on oeis4.)