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A062407 Numbers of the form Sum_{j=1..k} sigma(j) that are square. 2
1, 4, 2304, 24964, 73441, 1560001, 132549169, 1626428241, 147805647025, 3518227981636, 120105730444176, 1760865925304929, 1455206977344160000, 23275351872778367961, 17074391403452830178209, 26164085055965187661456, 37159616101199155480921 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(15) > 2*10^21. - Donovan Johnson, Feb 17 2010

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..20

PROG

(PARI) for(n=1, 3000, x=sum(k=1, n, sigma(k)); if(issquare(x), print1(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)) ) } \\ Harry J. Smith, Aug 07 2009

CROSSREFS

Intersection of A000290 and A024916.

Cf. A130698 (for the integers k).

Sequence in context: A172941 A180993 A192889 * A212799 A343695 A097476

Adjacent sequences: A062404 A062405 A062406 * A062408 A062409 A062410

KEYWORD

nonn

AUTHOR

Jason Earls, Jul 08 2001

EXTENSIONS

Terms a(7) and a(8) added by Harry J. Smith, Aug 07 2009

a(9)-a(14) from Donovan Johnson, Feb 17 2010

a(15)-a(17) from Giovanni Resta, Nov 22 2019

STATUS

approved

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Last modified February 3 09:09 EST 2023. Contains 360034 sequences. (Running on oeis4.)