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A062407
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Sum_{k=1..n} sigma(k) is a square.
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0
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1, 4, 2304, 24964, 73441, 1560001, 132549169, 1626428241, 147805647025, 3518227981636, 120105730444176, 1760865925304929, 1455206977344160000, 23275351872778367961
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(15) > 2*10^21. [From Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 17 2010]
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PROG
| (PARI) for(n=1, 3000, x=sum(k=1, n, sigma(k)); if(issquare(x), print(x), ))
(PARI) { n=0; for (m=1, 10^5, x=sum(k=1, m, sigma(k)); if (issquare(x), write("b062407.txt", n++, " ", x); if (n==8, break)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 07 2009]
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CROSSREFS
| Sequence in context: A172941 A180993 A192889 * A097476 A047676 A079187
Adjacent sequences: A062404 A062405 A062406 * A062408 A062409 A062410
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Jul 08 2001
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EXTENSIONS
| Terms a(7) and a(8) added by Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 07 2009
a(9)-a(14) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 17 2010
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