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Search: id:A100409
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| A100409 |
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Numbers n such that n is d_1*d_2*...*d_k-th composite number (n=A002808(d_1*d_2*...*d_k)) where d_1 d_2 ... d_k is the decimal expansion of n. |
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1
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OFFSET
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1,1
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COMMENT
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If n is a composite number then A002808(n-pi(n)-1)=n.
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EXAMPLE
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98 is in the sequence because 9*8=72 and 98 is 72-th composite number(98=A002808(9*8)).
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MATHEMATICA
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Do[h=IntegerDigits[n]; l=Length[h]; If[ !PrimeQ[n]&& n-PrimePi[n]-1==Product[h[[k]], {k, l}], v=Append[v, n]; Print[n]], {n, 100000}]
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CROSSREFS
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Cf. A002808.
Sequence in context: A108098 A114505 A045072 this_sequence A043157 A039334 A043937
Adjacent sequences: A100406 A100407 A100408 this_sequence A100410 A100411 A100412
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KEYWORD
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base,fini,full,nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 06 2004
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