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A320878
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Primes such that iteration of A062028 (n + its digit sum) yields 6 primes in a row.
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7
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286330897, 286330943, 388098901, 955201943, 1776186851, 1854778853, 2559495863, 2647782901, 3517793911, 3628857863, 3866728909, 3974453911, 4167637819, 4269837799, 5083007887, 5362197829, 5642510933, 6034811933, 8180784851, 8214319903
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OFFSET
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1,1
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COMMENTS
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In contrast to A048523, ..., A048527, this definition uses "at least" for the number of successive primes. This allows easier computation of subsequences of terms which yield even more primes in a row.
One can nonetheless compute the terms of this sequence by considering possible pre-images under A062028 of terms of A048527. This gives the terms which yield exactly 6 primes in a row (i.e., A320878 \ A320879), and one has to take the union with further iterates of this procedure (which successively yields A320879 \ A320880, etc).
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LINKS
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FORMULA
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PROG
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(PARI) is_A320878(n, p=n)={for(i=1, 6, isprime(p=A062028(p))||return); isprime(n)}
forprime(p=286e6, , is_A320878(p)&& print1(p", "))
/* much faster, using the precomputed array A048527, as follows: */
PP(n)=select(p->p+sumdigits(p)==n, primes([n-9*#digits(n), n-2])) \\ Returns list of prime predecessors for A062028. (PP(n) nonempty <=> n in A320881.)
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CROSSREFS
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a(1) = A090009(7) = start of first chain of 7 primes under iteration of A062028.
Cf. A230093 (number of m s.th. m + (sum of digits of m) = n) and references there.
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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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