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A257279
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Zeroless prime powers p^m with p <= m.
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2
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4, 8, 16, 27, 32, 64, 81, 128, 243, 256, 512, 729, 2187, 3125, 6561, 8192, 15625, 16384, 19683, 32768, 65536, 78125, 177147, 262144, 524288, 531441, 823543, 1594323, 1953125, 4782969, 9765625, 16777216, 33554432, 48828125, 134217728, 268435456, 282475249, 1162261467
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OFFSET
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1,1
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COMMENTS
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A few years ago, challenges had been launched to find a prime power p^n, n>1 as large as possible, cf. links. I have remarked that it is easy to find arbitrarily large examples by taking the square of very large primes, rather than high powers of smaller primes, and suggested a merit function to take into account and penalize such "trivial" solutions. This led to a new challenge including the condition n > p. This sequence lists such numbers with the last condition relaxed to n >= p, which is sufficient to make the search nontrivial but includes a few more terms, namely the zeroless powers p^p (A051674 intersect A052382).
Possibly is a(80) = 19^44 the largest term; there are no greater ones in the first 500000 terms of A257278. - Reinhard Zumkeller, May 01 2015
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LINKS
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S. S. Gupta, Can you find?, CYF n° 410 (Jan. 26, 2010) and CYF n° 412 (Nov. 13, 2012).
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PROG
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(PARI) is(n)=vecmin(digits(n)) && isprimepower(n, &n)>=n
(PARI) L=List(); lim=10; forprime(p=1, lim, for(n=p, lim*log(lim)\log(p), listput(L, p^n))); listsort(select(n->vecmin(digits(n)), L));
(Haskell)
a257279 n = a257279_list !! (n-1)
a257279_list = filter ((== 1) . a168046) a257278_list
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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