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A116051 n+sigma(n)+sigma(sigma(n)) is a semiprime (A001358). 1
2, 3, 6, 11, 13, 17, 20, 33, 39, 45, 47, 52, 57, 58, 59, 61, 63, 64, 69, 81, 83, 85, 86, 89, 91, 98, 100, 103, 110, 115, 117, 123, 128, 133, 134, 135, 136, 141, 142, 143, 144, 145, 149, 150, 153, 154, 156, 158, 162, 164, 167, 173, 179, 181, 184, 185, 187, 189 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..58.

EXAMPLE

115 + sigma(115) + sigma(sigma(115)) = 662 = 2*331

CROSSREFS

Cf. A001358.

Sequence in context: A152038 A105614 A116441 * A124593 A125882 A057758

Adjacent sequences:  A116048 A116049 A116050 * A116052 A116053 A116054

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 13 2006

STATUS

approved

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Last modified December 6 13:45 EST 2021. Contains 349563 sequences. (Running on oeis4.)