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1, 3, 7, 13, 21, 33, 49, 67, 91, 123, 159, 207, 261, 325, 397, 493, 601, 729, 873, 1035, 1227, 1443, 1699, 1987, 2311, 2695, 3127, 3613, 4125, 4701, 5349, 6117, 6981, 7953, 8977, 10129, 11425, 12883, 14419, 16147, 18091, 20139, 22443, 25035, 27951, 31023
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OFFSET
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1,2
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COMMENTS
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Partial sums of numbers n such that phi(n) divides n. The subsequence of primes in this partial sum begins: 3, 7, 13, 67, 397, 601, 1699, 1987, 2311, 3613, 14419, 42463.
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LINKS
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FORMULA
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a(n) = SUM[i=1..n] A007694(i) = SUM[i=1..n] {Numbers i such that phi(i) divides i}.
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EXAMPLE
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a(49) = 1 + 2 + 4 + 6 + 8 + 12 + 16 + 18 + 24 + 32 + 36 + 48 + 54 + 64 + 72 + 96 + 108 + 128 + 144 + 162 + 192 + 216 + 256 + 288 + 324 + 384 + 432 + 486 + 512 + 576 + 648 + 768 + 864 + 972 + 1024 + 1152 + 1296 + 1458 + 1536 + 1728 + 1944 + 2048 + 2304 + 2592 + 2916 + 3072 + 3456 + 3888 + 4096 = 42463 is prime.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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