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Search: id:A070026
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| A070026 |
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Initial, all intermediate and final iterated sums of digits of n are primes. |
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+0
2
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| 2, 3, 5, 7, 11, 14, 16, 20, 21, 23, 25, 29, 30, 32, 34, 38, 41, 43, 47, 50, 52, 56, 61, 65, 70, 74, 83, 92, 101, 102, 104, 106, 110, 111, 113, 115, 119, 120, 122, 124, 128, 131, 133, 137, 140, 142, 146, 151, 155, 160, 164, 173, 182, 191, 200, 201, 203, 205, 209
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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2999 = A062802(4) is the smallest term of this sequence for which the second iterated sum of digits is not the final sum; i.e. the smallest requiring three summations (2+9+9+9=29, 2+9=11, 1+1=2 and all three sums are prime). (The corresponding statement about the very large A062802(5) is not true because a large number of smaller nonprimes of the same digit length also have the digit sum 2999, the least being 29999..., where 333 9's follow the 2.). A062802, a sequence of primes, is a subsequence of this sequence and of A070027.
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EXAMPLE
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47 is here because 4+7=11 and 11 is prime while also 1+1=2 and 2 is prime. 39 (in A028835) is not a term: 3+9=12 is not prime - although 1+2=3 is prime. 49 (in A028834) is not a term: 4+9=13 is prime but 1+3=4 is not prime.
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CROSSREFS
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Cf. A028834 (Initial sum is prime), A028835 (Final sum is prime), A062802, A070027 (Primes from this sequence).
Sequence in context: A029979 A029981 A029982 this_sequence A036608 A136185 A026812
Adjacent sequences: A070023 A070024 A070025 this_sequence A070027 A070028 A070029
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KEYWORD
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base,easy,nonn
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AUTHOR
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Rick L. Shepherd (rshepherd2(AT)hotmail.com), Apr 13 2002
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