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 A147624 Numbers n = concat(a,b) such that omega(n) = omega(a) * omega(b), where omega = A001221. 3

%I

%S 23,25,26,27,29,32,36,37,43,46,47,49,53,56,59,62,63,65,68,69,73,76,79,

%T 83,86,89,96,97,104,108,113,116,122,123,124,129,136,137,139,142,143,

%U 144,145,147,148,152,153,155,158,159,163,166,167,169,173,176,179,183,184

%N Numbers n = concat(a,b) such that omega(n) = omega(a) * omega(b), where omega = A001221.

%C Concat(a,b) means decimal concatenation of a and b, i.e., a*10^[log[10](b)+1] + b, since we don't allow leading zeros in b.

%e a(1)=23 is in the sequence since omega(23) = 1 = 1*1 = omega(2)*omega(3).

%e 307 is not in this sequence although omega(307) = 1 = 1*1 = omega(3)*omega(07), since we don't allow leading zeros in the second part b.

%o (PARI) is_A147624(n)={ local(p=1, o=omega(n)); while( n>p*=10, n%p*10<p & next; o == omega( n\p )*omega( n%p ) & return(1))}

%o for( n=1,999, is_A147624(n) & print1(n","))

%Y Cf. A001221, A147616 (analog for sigma), A147619 (analog for eulerphi), A147627 (analog for bigomega).

%K base,easy,nonn

%O 1,1

%A _M. F. Hasler_, Nov 08 2008

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Last modified April 20 06:36 EDT 2019. Contains 322294 sequences. (Running on oeis4.)