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A126105
Prime(n)^2*prime(n+1)...*prime(a(n)) is the least product of consecutive primes which is abundant. Note that only the first term is squared.
1
2, 5, 10, 20, 34, 50, 72, 97, 129, 165, 203, 248, 295, 346, 405, 469, 537, 607, 685, 766, 853, 949, 1049, 1155, 1264, 1376, 1494, 1620, 1754, 1897, 2048, 2193, 2346, 2503, 2669, 2836, 3012, 3193, 3378, 3572, 3770, 3973, 4186, 4400, 4624, 4855, 5098, 5339, 5578
OFFSET
1,1
LINKS
EXAMPLE
a(3)=10 since x=5^2*7*11*13*17*19*23*29=5391411025 is abundant with sigma(x)=10799308800 and sigma(x)-2*x=16486750.
MATHEMATICA
a[n_] := Module[{p = Prime[n]}, c = 1; pr = 1 + 1/p + 1/p^2; While[pr < 2, p = NextPrime[p]; pr *= (1 + 1/p); c++]; c + n - 1]; Array[a, 50] (* Amiram Eldar, Aug 14 2019 *)
CROSSREFS
Cf. A005101, A007684 (a very similar sequence), A007708, A007741.
Sequence in context: A039690 A243938 A365630 * A117486 A263002 A325649
KEYWORD
less,nonn
AUTHOR
Walter Kehowski, Mar 04 2007
EXTENSIONS
More terms from Stefan Steinerberger, May 11 2007
a(21) corrected and more terms added by Amiram Eldar, Aug 14 2019
STATUS
approved