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A299145
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Primes of the form j^k + (j-1)^k + ... + 2^k, for j > 1 and k > 0.
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1
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2, 5, 13, 29, 97, 139, 353, 4889, 72353, 353815699, 42065402653, 84998999651, 102769130749, 15622297824266188673, 28101527071305611527, 20896779938941631284493075599148668795944697935466419104293, 105312291668560568089831550410013687058921146068446092937783402353
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OFFSET
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1,1
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COMMENTS
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Except for the terms 2, 5, 13, 29, 139, the exponent k satisfies k >= 4. More generally, if Q(j) = j^k + (j-1)^k + ... + 2^k is a term, then j-1 is a divisor of A064538(k). This is because (j-1) is a factor of Q(j) and thus Q(j) is prime only if j-1 is a divisor of the denominator of Q(j), i.e. A064538(k). Thus for each k there is only a finite number of values of j to check. This provides an efficient algorithm to find terms of this sequence by looking only for primes in the numbers H_{j,-k) - 1 = j^k + (j-1)^k + ... + 2^k for j-1 a divisor of A064538(k). - Chai Wah Wu, Mar 06 2018
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LINKS
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EXAMPLE
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2 = 2^1;
5 = 3^1 + 2^1;
13 = 3^2 + 2^2;
29 = 4^2 + 3^2 + 2^2;
97 = 3^4 + 2^4;
139 = 7^2 + 6^2 + 5^2 + 4^2 + 3^2 + 2^2;
353 = 4^4 + 3^4 + 2^4;
4889 = 4^6 + 3^6 + 2^6;
72353 = 4^8 + 3^8 + 2^8;
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MATHEMATICA
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With[{nn = 350}, Sort@ Flatten@ Map[Select[#, PrimeQ] &, Table[Total[Range[j, 1, -1]^k] - 1, {j, 2, nn}, {k, nn - j}]]] (* Michael De Vlieger, Feb 03 2018 *)
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PROG
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(PARI) limit=100000; v=vector(limit); for(n=1, ceil((-1+(1+8*limit)^(1/2))/2), for(k=1, logint(limit, n+0^(n-1)), a=sum(i=1, n, i^k)-1; if(isprime(a)&&a<limit+1, v[a]=1, ))); for(a=1, limit, if(v[a], print1(a", ")))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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