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A295076 Numbers n > 1 such that n and sigma(n) have the same smallest prime factor. 1
6, 10, 12, 14, 20, 22, 24, 26, 28, 30, 34, 38, 40, 42, 44, 46, 48, 52, 54, 56, 58, 60, 62, 66, 68, 70, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 130, 132, 134, 136, 138, 140, 142, 146, 148 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Supersequence of A088829; this sequence contains also odd numbers: 441, 1521, 3249, 3969, 8649, 11025, ...

Even terms of A000396 (perfect numbers) are a subsequence.

Subsequence of A295078.

Numbers n such that A020639(n) = A020639(sigma(n)).

Numbers n such that A020639(n) = A071189(n).

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

30 = 2*3*5 and sigma(30) = 72 = 2^3*3^2 hence 30 is in the sequence.

MAPLE

select(t -> min(numtheory:-factorset(t))=min(numtheory:-factorset(numtheory:-sigma(t))), [$2..1000]); # Robert Israel, Nov 14 2017

MATHEMATICA

Rest@ Select[Range@ 150, SameQ @@ Map[FactorInteger[#][[1, 1]] &, {#, DivisorSigma[1, #]}] &] (* Michael De Vlieger, Nov 13 2017 *)

PROG

(MAGMA) [n: n in [2..1000000] | Minimum(PrimeDivisors(SumOfDivisors(n))) eq Minimum(PrimeDivisors(n))]

(PARI) isok(n) = factor(n)[1, 1] == factor(sigma(n))[1, 1]; \\ Michel Marcus, Nov 14 2017

CROSSREFS

Cf. A000203, A020639, A071189, A088829, A295078.

Cf. A071834 (numbers n such that n and sigma(n) have the same largest prime factor).

Sequence in context: A175397 A129493 A036350 * A088829 A036348 A100368

Adjacent sequences:  A295073 A295074 A295075 * A295077 A295078 A295079

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Nov 13 2017

EXTENSIONS

Added n>1 to definition - N. J. A. Sloane, Feb 03 2018

STATUS

approved

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Last modified February 19 10:34 EST 2019. Contains 320310 sequences. (Running on oeis4.)